His key mistakes:
- Used a type of 1080 which came from a cluster he had previously supplied to Landcare
- Sent a retraction letter directly to the cop who interviewed him, allowing them to realise it was probably from one of the suspects that cop had interviewed
- Left DNA on the 2nd letter
- Didn’t shred a 2nd unsent retraction letter
The Police obviously did a very thorough job, and the testing of the 1080 to narrow down the batch would have been a huge help in getting the suspect list down from 2,600 to 60.
Kerr sending the retraction letter was a huge mistake. He was obviously spooked after being interviewed. But very dumb to send it directly to the officer who interviewed him, as that really narrowed it down.