I can admit to being in denial. Had a friend accused of a crime. I supported him. He was guilty. Had blinders on. Feel awful to this day.
I think it's how you're raised, dysfunctional garbage, abandonment issues, wanting to be a part of a "unit", fighting the "good" fight, "Timmy would never do that, he's such a good church boy" denial, longtime emotional investment in an individual, general dislike for law enforcement, or being conned into believing that person, either because you WANT to, or you're gullible and naive.
I don't understand it, and I went through it with my 1st ex. Multiple felon, heroin addict. Marriage lasted 6 years, half of which he was locked up in one place or another.
Domestic abuse was part of it, our daughter another, both of which made me tough it out and eventually divorce his sorry ***. He did make an attempt to kill me (again) when he got early release after the divorce, he was just a barrel of laughs that one.
Our daughter created a relationship with him a few years back. She's married and has 3 children, the oldest being 17. She knows his game and doesn't get sucked into it. Her kids are pretty astute also, they know he's full of it.
I would consider him a con of cons. His BIL (retired LE) always told him "You can't snow the snowman" when ever my ex tried to pull a fast one.