Property Abandonment- when is it mine?

In mid-May my roommates had a house party while I was out of town and several bands played. When I got back in town there was still lots of crap from the party in the basement that belonged to the bands. Guitars, Amps, Speakers etc. One of the bands came back in a few days and cleared all there gear...

However, I have a large mixing board, outboard gear, an entire pretty nice PA, a custom MESA cab, and some nice cases to pack it all in.

I asked my roommates to contact someone to pick it up because occasionally our basement floods and I don't want to deal with their crap getting messed up.

They contacted their primary contact for one of the bands who knew another band and told them to come get it. No one came.

My roommates tried again and now that other group is supposedly MIA.

After how long can we claim this stuff?

Also, my lease is up at the end of next month and I know if I leave it here, I'm assuming it would become property of my landlord. If we take it are there grounds for theft if they show up wanting their crap?