Your right but until he got involved he was just a bystander ?
It's not like he was helping them when he realise what they were doing he just stood there it was only when it got out of hand he step in so technically at that point he realised he wasn't innocent any more
. How exactly could he walk away he would got caught so he really couldn't walk away. He was already on probation with that investigator this would made him guilty by association.