With a little country like ours currently in the grip of Thomas/Lundy/Bain/Watson/McDonald/Tamihere/Rewa fever, a single thread on NZ murder mysteries would have been a better plan, but hey.
"Perhaps there was a mix-up of the hairs at the ESR laboratory?
Ah, the hair. Long since been my favourite piece of evidence.
All the experts called, and the one thing Watson needed was a gambler to explain that "30,000 : 1" odds of someone having the same hair type as Olivia.
Piece of cake. A gambler could easily explain to a jury that the odds of two people having identical hair at Furneaux Lodge were around 40%.
The maths to work out a pair in a chance of 1/30,000 is as follows: (reduced by factor of 100 for simplicity)
1/30 + 1/29 + 1/28 + 1/27 + 1/26 + 1/25 + 1/24 + 1/23 + 1/22 + 1/21 = 39.7%. On that basis, the chance of any one person having exactly the same hair as another person at the party was 39.7% likely. (The chances of two specific people having the same hair type are still 30,000 : 1, but selling the idea that there is a 40% of any person sharing hair type with someone else at the party is going to firmly lodge in jurors' minds.
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The scuttlebutt I have on Watson - and I don't even know whether the crime existed, but someone may do - is that the cops had a hard on for Watson because they were convinced he'd raped a woman on an island in the sounds.
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Something I forgot to include. The above-mentioned rapist - who was actively raping at the time of Ben & Olivia's murders - was also a Blenheim resident. If the cops hadn't had such a need for Watson, they may have looked at that bloke. One of his convictions relates to a rape on his boat in the Sounds, too.