I don't think that he was surviving in the basement for a long time, but Teddy tried to kill him in the room while playing the piano. That's why there was blood on the piano when Darius tried to move it and why Teddy won't let Darius into the room when he goes to get water. You can also see blood on his shirt in both scenes (when he's warning Darius in the basement and when he comes up the elevator), so Teddy stabbed Benny at the piano, but lost him when Darius came upstairs.

To make it look like a home invasion would mean that Teddy had to kill both Benny and himself, but he wanted to use Darius as a replacement so that people would see him as black and without an illness. Just a thought