Len was a fan of the Lizzie Borden ghost urban legend and could usually be seen outside the Borden house, trying to catch a glimpse of her ghost using spirit photography. He was a bit quirky, but otherwise had a normal life, friends and interests.
While Dean is checking the Lizzie Borden house for any supernatural activity, he notices a strange flash of light from a window, when he looks out of the window, a bright flash blinds him. Len is startled by Dean and runs away clumsily with his antique camera and tripod. After the murder of Mrs. Kemper, Detective Madsen identifies Len as the person Dean saw outside the window, commenting that he is harmless, just obsessed with ghosts. When another axe murder happens, Sam decides to look into that while Dean goes to question Len.
In Len's mobile home Dean questions him as to why he was at the B&B, he tells him he was trying to capture Lizzie with spirit photography. They are interrupted when Len's computer indicates a live chat room is open, he excuses himself to shut it down. As Dean is looking around and notices a drawing of the Mark of Cain on a piece of paper on the coffee table. He picks it up and shows it to Len and questions him where he saw it. Len attempts to lie to Dean about seeing it online, but Dean is able to see through him and presses him again. Len finally admits he saw it on a little girl named Amara outside the Lizzie Borden house a few nights ago, he tells Dean they briefly talked about Lizzie Borden and Len decided speaking to an underage girl outside in the dark was inappropriate and decided to leave. Dean tells Len that Amara is a runaway and when Len begs to know why Dean is looking for her. Len reveals that she did something to him as he doesn't eat or sleep or dream, the things he used to like leave him cold and that he is just playing the part of who he was, like "fake it till you make it", and that he's like a "robot puppet-man". He tells Dean that he was at the house earlier hoping to find Amara and make her fix him.
The next day, Len accompanies Sam and Dean while the look for Dawn Pinski, assuming she is also soulless and murdered her husband. In the Impala, Len goes on about he feels different, telling Sam and Dean about how he can do things he would never have done before and he just doesn't care, and that it feels like something dark is hatching inside of him. He asks Dean if he and Sam actually know what's wrong with him, Dean gets out of Baby. He reaches back in to grab one of Len's hands then handcuffs him to the Impala, before telling him he doesn't have a soul.
As Sydney is about to kill Sam, she suddenly drops to the floor, revealing Len standing behind her with a hatchet, shocked that he actually killed her. Upstairs Len is sitting with a bandaged hand, telling Dean he only ripped off his thumb to see if he could do it, and that he felt nothing after killing Sydney or for saving Sam and Dean. Realizing he may kill again, he asks Dean to kill him. When Dean refuses, he offers to take the fall for the murders, believing he'll be better off in prison.
Sam receives a call from Detective Madsen alerting them that Len was murdered. He later learnt that Crowley has been sending out one of his minions to clean up after Amara by killing the soulless humans.