Hanssen trusted O'Neill because they were of the same religion?

Well, a deeply flawed Christian, anyway. I love to watch this movie for the subscript. Part of it was how Hanssen was intrigued with O'Neill. Maybe he felt that "saving" O'Neill and bringing him back to the Church would atone for some of his own sins.

"I'd never ask you to trust me. It's the cry of a guilty soul."

He was a Catholic, not necessarily a Christian. Catholicism is a religion (often misrepresented as Christianity) whereas true Christianity is a personal relationship with Christ. I'm not saying someone can't be both but someone going to church, whether catholic or owise, doesn't automatically make them a Christian. The same way someone who goes to Staples Center doesn't make them a Los Angeles Laker. Catholics have their own beliefs, rituals, traditions and laws and pray to ppl (Mary, the saints, etc) that cannot hear their prayers bcuz they're not God. They are beloved of course, but they were only human.

Whether or not Robert's relationship with God transcended his religion wasn't determined altho he did seem sincere about it. At the same time, he was a a highly conflicted person making poor decisions. Nobody is perfect including Christians and who knows if Robert has found repentance in prison.