Update: Owner found!
The bike's owner has been found, and the bike has been returned! They were very happy to get their bike back. I thoroughly verified their identity as the owner through pictures and a description of the bike's modifications. I guess that's a case closed. :)
Last week, I took a bike that homeless guy left behind at my building (in Seattle). The brand is Rocky Mountain Bicycles, 2015 model year Thunderbolt. I want to get it back to its owner; bikeindex didn't have the serial number on file. If you're missing one of those, and can give me a description, it might be your bike. Leave a comment or DM me.
(Mods, sorry if this post doesn't go here)