My dad used to provide mental health treatment to sex offenders in prison. He said in all his years in that job there was one guy he was convinced was falsely convicted. The guy had been deployed with the military to a combat zone. Brought a personal laptop he shared with his whole unit.
When he came back to the US he tossed it into a closet & forgot about it for awhile. Later had a bad breakup & his ex accused him of things. They searched his quarters & found CSAM on the laptop. He swears someone else who used it put it there, maybe even accidentally. My dad believed him.
Oof. Yeah, "I have no idea how it got there" is so often used as a defense by people who know goddamn well how it got there that it's often just not credible, but still, some people LEGITIMATELY have no idea how it got there!