She was found dead in Met's basement bathroom. While I would expect him to clean up, this still makes it more likely that he was involved.
And how about DNA evidence found under the slain child's fingernails, blood on Met's jacket? That's theoretically possible if she died by mistake, but it seems that he was involved in her death.

Looks like he was fleeing the scene.

But the problem with your question is that it's not binary. The trip may have been planned AND he was also fleeing the scene.