Considering the trouble RL faced as a consequence of his parole violation, I'm actually not surprised he tried to arrange an alibi that night and next morning while LE and other people were conducting a search for the girls, asking where everyone was at the time, etc. Even if he knew nothing about the girls, he knew he could get busted for driving. I don't know if he is a convicted felon, but owning firearms would also be in violation. Either way, he didn't even cover the time of the murder for himself, so I tend to think he was more concerned about his driving violation. Jmo.
What I'm curious about is why the FBI was so sure something with the crime was digitally documented. Was that a profiling thing alone, or was there something to tell them that? Does it have something to do with the staging, or "signatures"? It's not stated outright that they have evidence, only that through experience, they suspect this was done.