Category Archives: Thoughts

Jurors, proof and the death penalty

The problem seems to be that many jurors just do not have a proper conception and understanding of proof, and appeal courts show extreme deference to the judgement of jurors. So somebody can be convicted of murder based entirely on speculation rather than proof.

One sign is a trial of extreme length. That happens when there is no proof and it’s all guesswork what really happened, or worse it’s clear a person is innocent but they are still found guilty.

There is also evidence that jurors who are in favour of the death penalty are precisely those jurors who will convict when evidence of guilt is lacking, so the death penalty compounds the problem.

Originally posted as a comment on this post

Reporting crime

The large scale abuse of the women gymnasts by Larry Nasser has exposed a flaw in the way crimes are reported. Nasser was able to exploit a weakness to abuse a large number of young gymnasts without being arrested or prosecuted, even though many of the victims had complained to their parents and to authorities.

The issue is that a single complaint may not be sufficiently credible for law enforcement action to be taken, but if there are multiple reports which corroborate each other, then it is possible to bring a prosecution.

What would an ideal system look like? To encourage truthful reporting, I suggest an automated system where humans are not given access until a defendant is identified by the system, based on multiple independent reports. The reporting system should be programmed to prompt for relevant details, to allow the computer system to automatically see if there are independent reports which corroborate each other. When the computer system holding the reports identifies a probable crime and a defendant, this information should be automatically published (without identifying information) and police should consider the report and obtain a court order for further investigative action to be taken, and ultimately for a prosecution to be brought.

See also


Complex problems

A long trial, intended to establish a truth about the natural world “beyond a reasonable doubt” may be a complex problem.

By “complex problem” I mean some kind of puzzle where you need to be quite organised to keep a large number of details under control, where the solution is not obvious, where a problem needs to be broken down into smaller components, and each component needs to be carefully examined and considered separately. We have to do this with large problems, because the human brain simply cannot think about very many bits of information at one time.

Most people, in most jobs, will never or hardly ever encounter complex problems they are required to solve. I am not sure what you should call the required skill, perhaps analytical skill, although I am not sure that captures it.

This skill is needed in mathematics, where the proof of a non-trivial mathematical theorem has to be constructed from “lemmas” (which are minor theorems used during the proof construction ).

Mathematics  is similar to justice in that proof is the central concept, although of course mathematical proof has a different kind of certainty to it – mathematical certainty rather than legal certainty, which is usually built around the somewhat fuzzy concept of “reasonable doubt”, which is more akin to probability theory* than mathematical certainty.

But although mathematical proof is different to legal proof, there are still similar errors that can be made. False assumptions, clerical errors and errors that arise from our imperfect understanding of the extremely complex natural world, including human behaviour.

Analytical skill is also needed in engineering and computer programming. For example, software to control a large aircraft needs to be broken down into small components, there may be many thousands of such components in a large project.

People with very good “analytical skills” (for want of a better word) may be quite rare, and rarer still in jury pools where employers of people with very good analytical skills may be reluctant to release employees for long periods of time.

So there is a strong chance of serious error when a group of unskilled people are asked to analyse a complex problem.

There is no way to independently test if the jury solution to a criminal problem is correct. While aircraft can be carefully tested, to see if the solution works, there is no way to test the verdict of a jury. If it is wrong, the error may take decades to discover, or the error may never be discovered ( at least in a court of law ).

This could perhaps help explain why there are many wrongful convictions.

* It is reasonable to view the job of a juror as calculating a probability of innocence ( while incorporating uncertainties about the calculation itself into their reasoning in a conservative way ). A typical jury instruction would state “If you are firmly convinced that the defendant is guilty of the crime charged, you must find him/her guilty”. If a juror concludes the probability of innocence is very small, say less than 1% then it would be reasonable and rational to be “firmly convinced” of guilt, even though the required level of certainty is never made explicit in jury instructions, it is left to the personal interpretation of each juror.


Inductive reasoning and confirmation bias

In a criminal trial, the prosecution may offer circumstantial evidence which is less than conclusive, and suggest that an innocent explanation is unlikely, even though an innocent explanation is quite reasonable, and is not excluded by reliable evidence

People sometimes say “I don’t believe in coincidences”. The universe of potential suspicious circumstances may be very large, and we often cannot even say if a coincidence is likely or unlikely.

This is “inductive reasoning”. From the wikipedia article on inductive reasoning:

“As with deductive arguments, biases can distort the proper application of inductive argument, thereby preventing the reasoner from forming the most logical conclusion based on the clues. Examples of these biases include the availability heuristic, confirmation bias, and the predictable-world bias.”

Confirmation bias may set in when inductive arguments are made (whether implicitly as evidence is presented, or explicitly in closing arguments), and evidence that shows the prosecution case is improbable may be ignored as a result of confirmation bias.

I believe wrongful convictions can easily occur when ambiguous evidence is presented. It is quite natural for jurors to reason inductively, as inductive reasoning often produces good results, even though it is not reliable.

Prior Discussion which led to this post.



The truth about the US justice system

I think many people think the US justice system has safeguards and is designed to protect the rights of innocent people.

Superficially that’s true, but it’s administered by politicians who can bend the rules whenever it suits them, and make judgements that defy common sense but which are not “unconstitutional” (so not subject to Federal challenge).

So in practice, wrongful convictions are commonplace, in serious cases perhaps 4% of accused people are innocent. Solving serious crimes is a tricky business, and there are going to be lots of mistakes.

Prosecutors with a weak case like the death penalty, because

(a) It allows them to appeal to juror emotions more strongly. There is a stronger presumption of guilt.

(b) It slows the entire process down, so by the time the truth is revealed (if it is ever revealed), the prosecutor has probably moved on and is now a judge or in private practice, or retired or dead.

A criminal justice system is a necessity, but society should recognise that convictions are not and cannot ever be certain, however much a jury is exhorted to respect the principle of reasonable doubt. People can be easily fooled, it is human nature.

So it is inevitable that there will be wrongful convictions. What is wrong is to suggest that wrongful convictions do not and will not happen, and to have extreme sentences that are unnecessary and serve no useful purpose for society.

Ranting at Montgomery

Mostly nowadays I try to retain my cool. But for a laugh, here I am totally losing it during a press conference County Attorney Bill Montgomery gave where he defended the State’s only witness against Debra Milke, who was sent to death row for more than 20 years as a result of Armando Saldate’s perjury:


I am happy to report that Debra Milke was finally exonerated on 17th March 15, 2015 🙂