Louis Schanzer was a neighbor of Todd Alquist and former police officer. He attempted to help Neil Kandy and Casey search for money in Todd's apartment under the impression that they were police officers.
Lou briefly converses with Todd Alquist while Jesse hides in Todd's apartment. When Lou leaves, Todd expresses his annoyance with Lou's nosiness, especially since Lou wasn't supposed to be home at that time of day. Because of Lou's presence, Todd and Jesse are forced to wait until Lou goes bowling so they can move Sonia's body.
In present day, Jesse is nearly caught by Lou breaking into Todd's apartment, but manages to duck inside at the last second. When Neil and Casey break into Todd's apartment, Lou spots them and, thinking they're police officers because of their jackets, offers his assistance in the investigation, adding that he never trusted Todd. After the pair capture Jesse, Lou knocks on the door wondering about the noise. He once again offers his assistance in the investigation, and tells Casey about a note Todd had left him that might be of use, forcing Casey to follow Lou to his apartment to keep up the ruse. Meanwhile, Jesse convinces Neil to hand over 1/3 of Todd's cash, since if he shoots Jesse, he will also be forced to kill Lou and any other witness.