Thursday, 26 May 2016

Using Bayesian networks to assess new forensic evidence in an appeal case


If new forensic evidence becomes available after a conviction how do lawyers determine whether it raises sufficient questions about the verdict in order to launch an appeal? It turns out that there is no systematic framework to help lawyers do this. But a paper published today by Nadine Smit and colleagues in Crime Science presents such a framework driven by a recent case, in which a defendant was convicted primarily on the basis of sound evidence, but where subsequent analysis of the evidence revealed additional sounds that were not considered during the trial.

From the case documentation, we know the following:
  • A baby was injured during an incident on the top floor of a house
  • Blood from the baby was found on the wall in one of the rooms upstairs
  • On an audio recording of the emergency telephone call made by the suspect, a scraping sound (allegedly indicating scraping blood off a wall) can be heard
  • The suspect was charged with attempted murder 
The audio evidence played a significant role in the trial. But, during the appeal preparation process, the call was re-analysed by an audio expert on behalf of the defence, and four other sounds were identified on the same recording that, according to the expert, showed similarities to the original sound. In particular, one of these sounds was of interest because of background noise that could be heard simultaneously. The background noise was presumed to be the television, which was located in a different room to where the prosecution argued the scraping of the blood took place.  During this second sound, the TV (located downstairs) could be heard simultaneously on the emergency recording. A statement by the police reads that the suspect was frequently rubbing his face in their presence. The defence proposed that the incriminating sound in the recording was not blood scraping after all, but simply the defendant rubbing his face.

The framework described in Smit's paper is intended to overcome the gap between what is generally known from scientific analyses and what is hypothesized in a legal setting. It is based on Bayesian networks (BNs) which are a structured and understandable way to evaluate the evidence in the specific case context and present it in a clear manner in court. However, BN methods are often criticised for not being sufficiently transparent for legal professionals. To address this concern the paper shows the extent to which the reasoning and decisions of the particular case can be made explicit and transparent. The BN approach enables us to clearly define the relevant propositions and evidence, and uses sensitivity analysis to assess the impact of the evidence under different prior assumptions. The results show that such a framework is suitable to identify information that is currently missing, and clearly crucial for a valid and complete reasoning process. Furthermore, a method is provided whereby BNs can serve as a guide to not only reason with incomplete evidence in forensic cases, but also identify very specific research questions that should be addressed to extend the evidence base to solve similar issues in the future.

Full citation:
Smit, N. M., Lagnado, D. A., Morgan, R. M., & Fenton, N. E. (2016). "An investigation of the application of Bayesian networks to case assessment in an appeal case". Crime Science, 2016, 5: 9, DOI 10.1186/s40163-016-0057-6 (open source). Published version pdf.
The research was funded by the Engineering and Physical Sciences Research Council of the UK through the Security Science Doctoral Research Training Centre (UCL SECReT) based at University College London (EP/G037264/1), and the European Research Council (ERC-2013-AdG339182-BAYES_KNOWLEDGE). 

The BN model (which is fully spceified in the paper) was built and run using the free version of AgenaRisk.

2 comments:

  1. A HEART OVER INDEBTED AND FULL OF GRATITUDE TO DR OGUDU THE MIGHTIEST LOTTERY SPELL CASTER IN THE WORLD
    My name is JOHN REHM It all started 2 years ago when i lost my job, and things became so hard for me and my family living in Florida and i decided to use my little savings to purchase a Florida lottery which never yield a result, I was now leaving in total mess and much debt i promised myself that i will never play the lottery again, After months of joblessness i was reading a tread online about{ DR OGUDU THE LOTTERY SPELL CASTER} and how he has made so many people to win the lottery, I for one don,t believe in magic and black powers but because i was very frustrated and stranded i decided to contact him through his email address, He demanded for few details about me which i gave him under 48 hours he gave me some numbers to play which have changed my life today.i was in a bar drinking when Florida Lottery announces that MR JOHN REHM is the sole winner of the 1,000,000 million POWER BALL jackpot from the drawing held on Wednesday, January 26, should claimed the prize at Lottery Headquarters in Tallahassee. if you,re in need of such winnings contact him via [OGUDUSPELLTEMPLE@YAHOO.COM] OR WHATS-APP HIM +2348106058254


    A HEART OVER INDEBTED AND FULL OF GRATITUDE TO DR OGUDU THE MIGHTIEST LOTTERY SPELL CASTER IN THE WORLD
    My name is JOHN REHM It all started 2 years ago when i lost my job, and things became so hard for me and my family living in Florida and i decided to use my little savings to purchase a Florida lottery which never yield a result, I was now leaving in total mess and much debt i promised myself that i will never play the lottery again, After months of joblessness i was reading a tread online about{ DR OGUDU THE LOTTERY SPELL CASTER} and how he has made so many people to win the lottery, I for one don,t believe in magic and black powers but because i was very frustrated and stranded i decided to contact him through his email address, He demanded for few details about me which i gave him under 48 hours he gave me some numbers to play which have changed my life today.i was in a bar drinking when Florida Lottery announces that MR JOHN REHM is the sole winner of the 1,000,000 million POWER BALL jackpot from the drawing held on Wednesday, January 26, should claimed the prize at Lottery Headquarters in Tallahassee. if you,re in need of such winnings contact him via [OGUDUSPELLTEMPLE@YAHOO.COM] OR WHATS-APP HIM +2348106058254

    ReplyDelete