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Attempt at Murder Sleuthing

Updated: May 18, 2022

I watched this documentary and became fascinated by the case. Michael Peterson was convicted of murdering his wife, having tried, according to the prosecution, to make it look like she fell down the stairs. He looked particularly guilty because a female acquaintance of his died in similar circumstances 20 years earlier.

"He looked particularly guilty because a female acquaintance of his died in similar circumstances"

It got my frazzled maths brain thinking: please forgive the morbidity, but if your spouse dies falling down the stairs (genuinely by accident, of course!) what is the probability that you know someone else who also died falling down the stairs by accident in the last 20 years? If Peterson's defence had shown the probability is quite high, he I think would have looked far less guilty.

In the UK, more than 1,000 people die each year falling down stairs (from a BBC news item). Let's assume it's more like 1,500 on the basis that some staircase deaths might be attributed otherwise. Let's also assume they're all accidents (big assumption!) Let's next assume they are all over 50, which means we only have to consider the 30% of the population who are over 50. Let's also assume that suspicions would be raised if the other person who died was one of your 100 closest friends.

By my reckoning, the probability of (at least) one of the 30,000 people who died in the last 20 years being one of your 100 closest friends is 14%. That's quite high (close to the probability of rolling a six!) and I suspect might have dispelled some of the jury's suspicions! Does anyone care to check my maths?

Published on LinkedIn

The views expressed in this communication are those of Peter Elston at the time of writing and are subject to change without notice. They do not constitute investment advice and whilst all reasonable efforts have been used to ensure the accuracy of the information contained in this communication, the reliability, completeness or accuracy of the content cannot be guaranteed. This communication provides information for professional use only and should not be relied upon by retail investors as the sole basis for investment.

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