Keys not returned and broken lease

[Remmy Vernon]

Had a tenant text me last week that he left his job in the area and would be out of his apartment by Oct.31st.

His lease ends the end of May 2016.

I reminded him that his lease was through May of 2016, and we would make every effort to rent it, but that he would be responsible for the rent till we got it rented or his lease expired.

He said he might know someone who would take it, then added that he would be moved out by the weekend and would leave the keys.

This weekend came and went. Went into the apartment, it was cleared out, VERY dirty, but no keys.   ( No noticeable damages at first glance. ) I didn't want to linger around just yet because to me, not leaving the keys says he still has possession. 

Texted him about the keys and whether he was out of the apartment or not and haven't heard a peep from him.  No forwarding address either.

I suspect he is having some bigger issues, hence the picking up and leaving so abruptly. Maybe legal issues, but I would only be speculating. He was a good tenant, and this incident, to me, is out of character. 

I'm just not sure how to proceed now.