Utah police suspect a teenager accused of luring a 12-year-old neighbor girl from her home and strangling her may have sexually assaulted the girl.

Search warrants unveiled Thursday show police in West Valley City investigated the case as a killing and sexual assault after they found the 12-year-old Kailey Vijil's naked body in a field with a shirt around her neck.

Prosecutors have charged the boy with aggravated murder but not sexual assault.

Salt Lake County District Attorney Sim Gill would not say Friday why the boy wasn't charged with the assault or whether the charge would be added.

The Associated Press is not naming the defendant because he is a juvenile.

A message left with the boy's attorney Friday was not immediately returned.