He admits to being a liar and a thief, on a gigantic scale – so he’s already facing a prison sentence exceeding his likely lifespan. Then he drops his alibi (admits he has been lying all along) and admits he was present at the murder scene close to the time of the murders.
If he was a Yid being tried by a Sanhedrin, he could convince them he is not guilty. If he had an serious alibi, he would have presented it. He can’t complain about the jury (he was a well known and locally respected celebrity), and the jury didn’t believe him. It should be noted he was NOT sentenced to death.