MovieChat Forums > Cold Justice (2013) Discussion > On Circumstantial Evidence

On Circumstantial Evidence

posted 9 years ago by Crentapa
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Now, let me first confess that I do not watch this show... but let me clarify that I am not backseat reviewing either. What I want to talk about is just a small issue people ignore with circumstantial evidence that the responses here show.

*How I got here was a curiosity on what the conviction rate was for the show, or if anyone turned around and sued the show. Basically how "effective" the team was at solving these crimes. Now back to circumstantial evidence.

I recently began rereading Holmes again and, for the fun of it, poking holes in his arguments. It is an entertaining mind exercise to test how strong the great Logician's argument's really are. What I noticed was something startling, to me at least:

When taken as individual pieces, Holmes' arguments are rather unsound. Since he mainly uses inferences (or Circumstantial Evidence) this means that each inference has a probability attached.

Not related to anything but let's say you find a fingerprint outside of a house that a murder occurred in, you then measure footprints to conclude how tall the killer might be, you then find a CUT (as in no DNA) piece of hair to claim the colour of the killer's hair.

If that fingerprint provides a person who fits the other two pieces of evidence, we fall under the conjunction fallacy in believing it is MORE LIKELY for the killer to have left the fingerprint ONLY on the outside (again, this is really made up and isn't anything to do with the show; just that I got inspired by the forums for this situation) but nowhere else than it is for a second unknown person to be involved who wore gloves.

Also note that the probability that the hair and the footprints belonged to the killer is unestablished. Just connecting these three incidents at a fixed 95% probability each means an 85.7% probability in total (Assuming a binomial, "Evidence belongs to killer", "Evidence belongs to someone else". Equation for binomial is just p1*p2*p3 or (0.95)^n in this case)

95% is lowballing quite a bit, given this type of evidence gets credibility from using "hard" evidence to increase the relevance. (Such as hair colour, checking out close relatives and family or co-workers who may have visited and firmly establishing that the hair "shouldn't be there".) But the problem is that before any of that credibility is established, the "clear linear path" seems obvious.

It also has me wondering, despite that it probably wouldn't fly in court (I am fairly certain the defense can "point at other suspects", but to do an all out case on someone who cannot defend themselves goes too far, I believe); if the public defender, instead of trying to prove his client is innocent, brought one of the suspects the police excluded and worked extremely hard to paint that suspect as guilty, how the jury would respond.

Excluding the cult of personality effect ("I just like X person better, thus his argument is better"), I would imagine the jury would end up a hung jury; no longer being able to keep things black and white. Which person is "more guilty" than the other?

[–] Crentapa 9 years ago

Eitherway, mostly just thoughts rambling in my brain and this just ended up being where I expressed them.

[–] simonxlong 9 years ago

Actually, accusing another party of committing the crime and essentially arguing how all of the evidence really points to them is a time honored tradition amongst criminal defense attorneys. Simply put, logic dictates that if their client didn't commit the crime, someone else must have. Simply finding a few anomilies and arguing the weight that should be given to different types of evidence isn't enough. You have to give the jury an alternate version of the crime.

This requires that the defense build another reasonable suspect that also fits, at least in part, the evidence. If the police have another strong suspect besides the defendant, the defense will often argue that the other suspect is really guilty. This is rarely the case however, because the prosecution doesn't prosecute until that other suspect can be eliminated from contention or until the evidence against the defendant is exceptionally strong. This often leaves the defense having to present an as yet unknown alternate second party as the potential guilty person.