Azimuth Myths

 

CM compass

There are three primary ways of determining where someone is by way of their phone records or CDRs (Call Detail Records):

  1. Mapping by way of the azimuths.  On a 3 sector tower (the most common type of cell tower) one divides the 360% coverage/circumference into 3 “pie slices” at 120% each. (0 & 360  on the circle are always due north.)  The “azimuth”, or center of the sector, is the center point of the “pie slice”, so if the azimuth is 85%, you would add 60 to one side of 85%, subtract 60 from the other side of 85%.  This would give you a slice ranging from 25% to 145% .  85 at the center and then the range spreading out from there.
  2. Mapping by way of a drive-test  This is achieved by utilizing a device that operates somewhat like a cellular handset driving a specific area and monitoring the dominant/probable and possible reach of radio frequencies and DB levels from the towers the device connects with (anyone can perform an informal drive test with their own phones, for the cell towers they ping).  [Drives tests were not invented to solve crimes, but are actually a method by which telecommunications companies can determine if they are providing adequate coverage for their clients/subscribers.]
  3. Global Positioning System or GPS-this is the most precise means of determining where someone is or was.  However most phones didn’t have GPS back in 2010.  So for the purposes of this case GPS is not available for determining the location of Chase Merritt. Or it seems, Joseph McStay-although Google phones might have been equipped with GPS.  Not sure.

 

How does a cellular phone choose which tower it connects with?

Witness for the prosecution, FBI agent, Kevin Boles stated that a phone will choose the tower that is most “attractive”.  As he clarifies in his testimony, in 2010 this “attractiveness” was largely due to strength of signal. (Apparently phones operate differently now.)

But what then determines the strength signal or (attractiveness) of a tower?

There are a lot of factors as to why a tower gives off a weak or strong signal for a particular subscriber, here are a few:

  1. Number of subscribers pinging.  So if there are a lot of people in an area–classic example is a tower near a ball park when a game is in progress–the tower can experience subscriber overload, and so even if that tower is closest, a subscriber will be “bumped” to a tower farther away from their physical location.
  2. Down-tilt.  Antennas are tilted to cover areas a phone company anticipates will require the most coverage.  What direction the down-tilt is, can mean that even if at tower is closer in physical location to a subscriber, if the antenna is focused away from them, they will then possibly find a tower farther in distance to have a stronger signal.
  3. Damage to the tower. If a tower is damaged, say in a storm, that can force a call to be bumped to a tower farther away.
  4. Frequency at which radio waves are operating. Radio waves operating at lower frequencies travel farther than those operating at higher frequencies.
  5. Obstruction to line of sight If there are physical obstructions between the subscriber and the cell tower, this can make a connection difficult, even if the tower is close by.
  6. Elevation. Kevin Boles testified at the grand jury hearing for Robert Pape (People v. Pape) that higher elevation (specifically of a tower) can allow for a subscriber at a lower elevation to a tower to ping from a much greater distance than expected.  Boles gives the example of being in San Bernardino and pinging a tower in the  Arrowhead mountains, 30 miles away (see below).

san-bernardino-arrowhead

Kevin Bole’s Testimony at Grand Jury Hearing

 

 

Below is a basic mapping of the three azimuths listed in the Bole’s exhibit.  Bole’s now states that only the first tower pinged counts, so the 330 azimuth may be moot.  But this does show the expected coverage for azimuths 10 and 85 in relation to the graves, and Oro Grande.  There is always the possibility though, that radio waves from an antenna travel beyond, or in different directions than anticipated, which is why drive tests reflect more accurately where a subscriber might have been, than just mapping the traditional “pie slice” range.

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Chase Merritt Tower Pings February 1, 2010

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Chase Merritt Tower Pings February 2, 2010

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Chase Merritt Tower Pings February 3, 2010

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Chase Merritt Tower Pings February 4, 2010

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Chase Merritt Tower Pings February 5, 2010

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Chase Merritt Tower Pings February 6, 2010

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The various towers pinged by Chase Merritt’s phone at the following times on Feb 6, 2010– 11:30, 11:31, 11:32, 11:33,11:34, 11:52, 11:53, 12:49 & 1:30 are as much as 10 miles distance from one another, and they ping in a random rather than linear order. Also note the difference in seizure vs. elapse time.

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Pic monkey CM Map 1 (1)

 

 

Example of drive-test vs. traditional cellular tower mapping. The colors each represent the reach of the sector.  Note that some coverage expands beyond the “pie” slice of expected reach, and coverage can pop up in unexpected locations.

drive test

How Cell Tower Triangulation Works

 

 

 

Resources

 

Caselaw/Drive Tests

Author Kevin Metcalf-Books on Cellular Mapping

Cell Tower Triangulation and Tracking Evidence — How It Works

Court Rejects Cell Site RF Map

The uses and abuses of Mobile Phone Evidence

What your cell phone can’t tell police

37 Comments

  1. This episode of Dateline could have something to offer around this case. https://www.nbcnews.com/dateline/video/the-girl-with-the-red-shoes-part-2-865967683760

    This case involved a spot, or “bowl” where the manner in which the phone of the victim pinged, made it look as if she was moving, when she actually was not. It makes no sense that Chase Merritt was at the graves when he made any of the calls on the 6th, because there was zero obstruction in the line of view from the graves to the towers on the Quartzite mountains. He should have had perfect reception if that’s where he had been. But instead all the pings to the Q mountains have long seizure times, almost half a minute, and the calls get immediately dropped once they connect. That’s more indicative of him being a distance away, where there are obstructions. The 85 azimuth could reach to Apple Valley. He could have been helping his brother run errands, any number of things. But he wasn’t at that grave site, or anywhere near it, probably.

    1. But it kind of looks like he’s at the graves for those pings. Doesn’t that azimuth have a east direction?

      1. It’s so hard to tell the exact azimuths, because we lost visual of the trial just as the defense brought their counterpoints to the analysis. But to me the towers on the Q mountain, almost have to have the best reach of any of the others. I can’t imagine those towers were designed to cover the areas near to the graves-no one lives there-and though there is a little traffic to that area, not much. So most likely the down tilt was to reach into places like Apple Valley and to give comprehensive coverage to those driving the 15.

        Which would explain why you might be in Apple Valley or downtown Victorville and happen to ping off towers on that mountain. And radio waves are not linear, they blob around. An azimuth signifies a basic, general direction, not an absolute.

        1. The 12:49 call is the only one that really gives Chase a connection, worth a damn. And that tower is downtown Victorville. I bet he was running errands with his brother that day.

          1. Chase could have stopped and got gas, bought groceries, etc as well but there’s no proof of that. For the sake of argument though, let’s go with that Bennett was helping Chase run errands. It all lines up.

            1. I do think that Chase running errands or doing something in Victorville or Apple Valley makes more sense, than that he is at the grave sites when those calls are made-for all kinds of reasons, including the difficulty of digging graves while you are constantly having to redial. When looking at all the pings during that time period, the strength of the signal is strongest at 12:49, and that tower is smack in the middle of downtown Victorville. That doesn’t necessarily mean he was exactly at that tower, but it would lead me to believe that there were no obstructions in the line of sight between Chase and that tower when that call was made.

              The calls Chase makes when he pings the towers on the Quartzite mountains ALL have very long “seizure” times (the time it takes for the call to connect) And what had to have been frustratingly short “elapse” times–which is the time that he actually connected to the person he was calling. What I would guess is that Chase was moving around, in order to make a successful call. We have to remember, this is 2010 and AT&T wasn’t as large a presence as a phone company in Cali at this time. Since then ATT&T has swallowed up Cingular and Bell, but back then, when I researched this in 2014, AT&T didn’t even have any of their own towers. Or at least none registered with the FCC. They were leasing.

              So they could have been leasing towers on Con Ed land or mom and pop set ups. Those towers may not have been all that well maintained, or been up to FCC standards, if they were below the elevation required to register with the FCC.

              i remember back in 2010 living in a major city, and I would sometimes have to walk a block to get good reception. Or only certain spots in my apartment had good signal. Now we have great reception, almost all the time. But back then, this wasn’t the case.

              For Chase to have his called dropped when he pings on the Quartzite mountains, I believe there had to have been an obstruction between those towers and where he physically was when he made those calls–say a building, or a wall, etc (if he were inside), and that is not the case at the graves. If you are at the graves, as Bole’s testified to and presented a diagram to show, there would have been zero obstruction between a caller at the graves and the towers located on the Quartzite mountains. In theory, someone calling from those graves should have had perfect reception.

              It’s a wonder no one tested for this. That no one actually went to the gravesite and made a call with an AT&T phone.

              1. LOL Why would he be dialing while digging? Could have been his carrier or that he was driving further and further away from the quartzite tower. But, as long as we both finally agree that Chase was in fact in VV that day, I’m good with that.

                1. Or he’s in Apple Valley. Those sector azimuths are consistent with this as well. But what I don’t think you appreciate, is that if the pings don’t place Chase at the graves, all this is, is evidence of a trip north, it’s not proof he was ever at those graves.

                    1. But the pings have to tie Chase to the graves. I know on Websleuths no support for anything stated is required, but in a court of law things have to be proven. Simply because Chase can’t recall why he was in Apple Valley or southern Victorville on that Saturday, isn’t proof he even knew the bodies were buried anywhere near where he was. In fact, we don’t have proof that the bodies were buried prior to the 12th.

                      The only reason those pings had any validity is if they showed Chase present at the site of the graves. Failing that, they are meaningless. If Chase lived in Chicago, and he pinged in Victorville on that Saturday, claiming he never left Illinois, that would be significant. But there could be so many innocent explanations for his pinging in downtown Victorville, that a hiccup in memory hardly qualifies as an indication of guilt.

                    2. It’s not that he couldn’t recall, he repeatedly told detectives he had not been there. Then his sister with remarkable recall (but can’t remember anything else toe save her life) speaks to Chase being around all the time. Great. But this is after he and Cathy separated and he had no place to live.

                    3. Chase said he couldn’t recall but if he’d been to Victorville that day it would have been to see his brother. Chase is not asked about February 6 until 4 years later.

                    4. Actually he never said he couldn’t recall, After questioning, he said he had siblings up there. He was reluctant in his questioning. It would seem to me he would be forthright in offering that info but he seemed held back.

                    5. The manner in which Chase is being questioned, it seems as if he is taking the question literally-as in, that he was never at the graves. Later he says if he had been in Victorville at all, it was to see his brother. He mentions his brother.

                2. The state has to tie Chase conclusively to a crime scene. So far they have failed to do this.

                    1. Then show me one piece of evidence that conclusively shows Chase at any known crime scene. Conclusive evidence. Irrefutable.

                    2. And this proves what? Are you claiming that there is only one person physically capable of drafting this check? What proves it wasn’t Joseph McStay? Not what you speculate about, what PROVES this assertion?

                    3. It proves aa great deal. For one, it’s for a client they are working on or will be. 2, the amount is almost the same for the one he creates the next day with the same memo. 3, it’s all “Chase Merritt” is all lowercase, typical of Chase. 4, it’s written shortly after a truck bearing a very striking resemblance to Merritt’s truck PULLING OUT of the Mcstay driveway. 5, The check is deleted. Why? Because Chase realized his folly, it places him there.

                      You can speculate it’s Joseph, but we know now how Joseph wrote checks, it never differentiate one from the other. Why start now? Why didn’t he give this check to Chase at lunch? Why did Chase reproduce the exact same check the next day?

                      Why is it he never told any of this check writing and backdating to LE, Mike, Susan, or Dan? You can’t separate these other checks from the first one, they are the same author.

                    4. All good points. However, you then have to make sense of the entire set of circumstances involved.

                      In order for Chase to have written that check on the 4th and for this to be related to the crime, then logically, Joseph McStay would have to either have been dead or incapacitated at that time. And for Joseph to be one of those two things, the rest of the family would have to have been as well (or there would have been someone running out the door for help or fighting Chase).

                      So where is the proof that the family was either dead or incapacitated at that time? There is another call that is made from Joseph’s phone, at 8:28PM, and it pings the usual tower he would ping if home. There is nothing to prove Joseph didn’t make that call.

                      1) Sometimes people just do things in a different way, the fact that an action is new doesn’t mean it is related to another novel event (say murder) in that person’s life. That connection has to be proven. Maybe Joseph was fixing a glitch in his new arrangement with Chase and check writing.

                      2) The fact that a truck that is thought to be Chase’s leaves BEFORE the check is written, can actually be listed as “reasons why that check couldn’t have been written by Chase”. If Chase’s truck already left, then how is he writing a check. What is there to show he came back? Why would he return? That needs to be explained. Or at least reasoned through. Is there a video of that?

                      And then there is the gigantic elephant in the room–it has absolutely not been proven that the truck captured by a neighbor’s surveillance was Chase’s. Also, that same neighbor testified that Joseph would park the Trooper backed into the drive-where was this truck that was videoed even parked? If you look at the neighbor’s camera angles all you can see is the front light beams, you cannot tell how far up the drive the truck was when those beams were caught on camera.

                      There has to be more.

            2. This doesn’t mean that Chase didn’t bury the bodies before he made those calls. Or another time. But the calls themselves prove nothing.

    1. I see them now. I’m not seeing a connection to what you’re implying. Can you expertly guide us through how Chase’s phone pings shows up in the 85 azimuth?

      1. I can’t. I don’t have time right now. But you can map it for yourself. It’s not that complicated. On the 6th there are a series of calls that bounce around, and the tower locations are on the map. Google map those locations.

        1. I’m aware of the cell tower locations. I’ve already provided a plausible explanation for the pinging of different tower s here on your blog.

          1. Btw, it would not be a “genius move” for Chase to turn his phone off at any point. It was common knowledge to phone users in 2010 that you could be tracked due to pinging towers.

            1. Why then would Chase speak for over half an hour at the graves, if he was aware of this?

                1. That’s not what the ping evidence is telling me, but again, if you are satisfied with your analysis. Nuff said.

          2. Well then you don’t need my input. If you are satisfied you’ve got this right, nuff said. Right?

  2. The fact that Chase’s phone connects and bounces off of 2 towers on the Quartzite mountains, and another two or even three that are miles away, at the most southern tip of Victorville, all these pings within an hour and half period (and the sequence is not in keeping with linear movement), actually makes it appear that he might have been as far as 10 miles south of the graves-and that he might have been indoors. And 10 miles south of the Quartzite mountain towers-which is why those calls don’t last for more than an instant. My reasoning behind this is that the tower that pings almost in Mountain View is likely at a lower elevation with less reach than the towers on the Q mountain range, which are at higher elevations with greater reach. But again, one would have to know all the factors related to those towers on that day-what was their down-tilt, were any towers damaged in the storm, what was subscriber traffic like, etc.? And a drive test would help in getting close to any accuracy with this.

  3. Azimuth for the 11:53 AM call on the 6th faced north west.

    It is possible to ping behind a sector.

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