Alexander Paul Pacheco was arrested Saturday, three days after Kelsey Shannon's body was found in a drainage ditch less than a mile from her home in Broomfield, The Denver Post reported.
Shannon disappeared Oct. 14 after arguing with her mother Dottie Shannon about her choice of friends, the Post reported Sunday.
On his MySpace Web page, Pacheco called himself "tha widowmaker" and wrote of his passion for night life, illegal drug use and violent gangs, the Post reported.
Pacheco, who was arrested in September for underage drinking and theft, denied knowing anything about his girlfriend's disappearance when police interviewed him last year, said Broomfield police Sgt. Mark Goodell.
The (Boulder) Colorado Daily Camera reported Adams County Coroner James Hibbard said pathologists used a partial fingerprint, dental records and items of clothing found at the scene to identify the teen's body. Hibbard's office was still working to determine the cause and time of her death.
"Due to the body being badly decomposed and out in the elements so long, it's going to be a little difficult to determine what caused this girl's death," Broomfield Police Chief Tom Deland said Friday.