Analyzing a Confession
Warning: this blog post contains spoilers for the Netflix documentary series Making a Murderer
Brendan Dassey’s confession
If you haven’t seen the true crime documentary series Making a Murderer yet, go watch it! The Netflix series gives a fascinating -yet disturbing- insight into the American justice system and how it seems to fail to adhere to the principle of guilty beyond reasonable doubt.
One of the most cringe worthy things we see in the documentary is the confession of Steven’s nephew, Brendan Dassey. Brendan is a boy with learning disabilities and is interrogated without any help present by two trained policemen (Fassbender and Wiegert) for 6 hours. In this interrogation Brendan confesses helping Steven Avery rape and murder Theresa Halbach. It is this confession alone that leads to his conviction for life and it helps in the conviction of Steven Avery. We see some parts of the interrogation in the documentary, such as the part below.
FASSBENDER: Did he say why he wanted you to do that?
BRENDAN: No. (shakes head “no”)
WIEGERT: Which knife did you use?
BRENDAN: The same one he stabbed her with.
FASASBENDER: And how many times did he stab her again?
FASSBENDER: Are you sure about that? (Brendan nods “yes”)
WIEGERT: So Steve stabs her first and then you cut her neck? (Brendan nods “yes”) What else happens to her in her head?
FASSBENDER: It’s extremely, extremely important you tell us this, for us to believe you.
WIEGERT: Come on Brendan, what else?
FASSBENDER: We know, we just need you to tell us.
BRENDAN: That’s all I can remember.
WIEGERT: All right, I’m just gonna come out and ask you. Who shot her in the head?
BRENDAN: He did.
FASSBENDER: Then why didn’t you tell us that?
BRENDAN: Cuz I couldn’t think of it.
4 hours of the interview can be seen here.
As it is kind of hard to analyze 4+ hours of video, I wanted to see if I could do some automatic analysis of the interview. The goal is to gain a little insight in the interrogation, in particular to what extent the detectives spoonfed the confession to Brendan.
Getting the data
Luckily, a PDF transcipt of the interview is available here. I downloaded the PDF and performed OCR (using Google Docs) to extract the text. I then did some very simple computational analyses of the text using Python.
Analyzing the most frequently used words by all parties, it becomes clear that Brendan acknowledges a lot of the questions asked to him. Frequent words for Fassbender are Brendan, tell, us. That seems about right. Also note that the detectives frequently use the words honest, truth, anything. This is something we also saw in the documentary: whenever Brendan tells the detectives a thing that doesn’t fit their narrative, they tell him to be honest and tell the truth, nutil he gets it ‘right’. Guessing, just like in school.
Words uttered during the interview
Next, we can have a look at the total words that are uttered during the interview.
Interesting is that both Fassbender and Wieger talk more than Brendan in the beginning of the interview, and that Fassbender seems to get be more prominent nearing the end. Brendan is very consistent, reaffirming his role as acknowledging. We can see that the interrogators together have uttered around 22.000 words while Brendan has only uttered 10.000.
###Unique words uttered during the interview
More interesting are the unique words uttered during the interrogation. Basically, repeating a word probably doesn’t bring new information into the conversation, so only looking at new words that haven’t been uttered by any of the parties before might give some more insight into who brings new info to the table.
As we see here, the difference becomes only bigger. Both detectives utter more new words than Brendan, roughly 1100 versus 450. Interesting is the beginning of the conversation, where both detectives are uttering a lot of new words and Brendan is not really adding all that much.
###Unique bigrams uttered during the interview
Words can take us only so far. There are a limited number of words that we can use, but we can use them to convey information in lots of ways: ‘Mary slaps John’ and ‘John slaps Mary’ contain the same words but have different meanings. So. let’s look at combination of words, so-called n-grams. Let’s look at all the unique pairs of consecutive words, called bigrams.
Interesting is that during the later stage of the interrogation Fassbender is adding a lot of new information to the conversation.
I did some very simple visualization of the Brendan Dassey interrogation. We can see that the detectives introduce lots of unique words and phrases to the conversation, which might indicate their very pro-active role in the interview. Of course there are a lot of things to consider. For example, many topics are discussed during the interrogation, not just the confession to the murder and rape. There might also be some noise in the data resulting from transcription and OCR errors. This analysis just paints a general picture. It would be interesting to compare this to other known false confessions and also compare to confessions that actually lead to new information which was verified by actual evidence. Would there be similar patterns? A lot more analyses could be performed on the data: measuring perplexity of the speakers (how predictable are their utterances?), topic modelling (who talks about what), etc.
Anyone who wants to dive in, go ahead: the Python notebook and the interrogation text file can be found here