Did you watch this? I sat down yesterday and gave my full attention to it to see if I could pick anything out. This guy was very interesting to say the least, body language wise!
I picked out a good few red flags and when put together would make clusters. Therefore If this guy was on trial again and the authorities knowing what they know now about body language, I feel he would be actually charged for the crime of killing the boy.
He went on the defensive very often and really only wanted to talk about certain things. If the Criminologist who was interviewing him went down a road of questions that he did not like then he would get defensive and angry.
My assessment, just from the information on the TV show would be the last scenario given is the most plausible. This being that he was colluding with the old farmer to steal antiques from The farm. Either the farmer killed the boy or Bert Spencer did but they were in it together and this is why Bert killed the farmer.
Its one of the crimes that will never be solved as I believe that Bert Spencer will take this to his death bed and never reveal what truly happen.