The difference between the two has a lot to do with the estimation of the "main routes of travel". When Stride is include, both Nichols' and Stride's locations are flagged as being "outliers" - meaning off the major route, and the estimation of the major route passes more vertically (sort of Eddowes to Chapman type thing). A few other calculations change as well, but those changes are more subtle (the output is, after all, influenced by the data you put in). One of the important things to get right is the crime linkage - while one would want an analysis like this to be robust against some erroneous inputs and/or omissions, the better the data the better chance of getting a useful output. At the moment, my analysis program's output is influenced if the map (the image file) doesn't contain a large enough area for the search (like this one; it's not big enough for even the red zones, and the green zones clearly extend off the map; there are two additional zones after that, which have to do with commuters - offenders who live outside the circle (outside the crime region as it's called). The image file really needs to have a large enough "surround" to plot all 4 of those zones, but really big images take a long time to process. Also, I'm still working on the underlying routines (this is all stuff being worked on and researched, and while so far the few tests I've been able to do with solved cases have been encouraging, the sample is too small to say anything other than it's worth continuing with).
For example, here's the BTK (Dennis Rader) output. The blue square near the top (in Park city) marks his residence, which is right in zone 1, and for this the image file is large enough to show all of zones 1-6, so those will be fine, but after that the details from zone 7 onwards will be slightly out, but we're seeing enough to get a good idea.
For the Golden State Killer (Joseph James DeAngelo), again, the map image file I have is undersized, so the zone boundaries are going to be off a bit once the zone extends "off screen". He's right on the border of zone2 and 3, but, provided the areas to the north don't contain part of zone 3 or better, that shouldn't change. At some point I'll need to get the program to deal with the "off image space", but there's a few other things that I need to focus on first. And yes, I fully admit, I'm showing the impressive ones, it's not perfect, and there are cases where it fails miserably. But, while the ideal would be to get something that is always right, for something as complex and individualistic as serial crimes, I would be happy with the more modest goal of getting something that much more often than not provides a better than chance search pattern. And it's only a suggested search pattern, geographical profiling doesn't "solve" crimes, it's just a tool that can be used by investigators as they work on solving the crimes. If they get leads on a suspect that doesn't live in a "suggested zone", then they should ignore the profile. These are useful to suggest where to start to search, particularly if leads are not forthcoming.
For example, here's the BTK (Dennis Rader) output. The blue square near the top (in Park city) marks his residence, which is right in zone 1, and for this the image file is large enough to show all of zones 1-6, so those will be fine, but after that the details from zone 7 onwards will be slightly out, but we're seeing enough to get a good idea.
For the Golden State Killer (Joseph James DeAngelo), again, the map image file I have is undersized, so the zone boundaries are going to be off a bit once the zone extends "off screen". He's right on the border of zone2 and 3, but, provided the areas to the north don't contain part of zone 3 or better, that shouldn't change. At some point I'll need to get the program to deal with the "off image space", but there's a few other things that I need to focus on first. And yes, I fully admit, I'm showing the impressive ones, it's not perfect, and there are cases where it fails miserably. But, while the ideal would be to get something that is always right, for something as complex and individualistic as serial crimes, I would be happy with the more modest goal of getting something that much more often than not provides a better than chance search pattern. And it's only a suggested search pattern, geographical profiling doesn't "solve" crimes, it's just a tool that can be used by investigators as they work on solving the crimes. If they get leads on a suspect that doesn't live in a "suggested zone", then they should ignore the profile. These are useful to suggest where to start to search, particularly if leads are not forthcoming.
Comment