The boy was arrested in December, aged 16, after Rouhselang's body was discovered in a dumpster behind a restaurant near her home. She was six months pregnant at the time.
Rouhselang's mother told police she had gone to speak with the father of her child. When she didn't return, her mother went to Trejo's house to ask him; he told her he was supposed to meet her in the alley but claimed she never turned up.
In police interviews, Trejo said he knew Rouhselang was pregnant and that he was "supposed to be the father of the baby". He claimed that they fought over it, and that she had waited too long to tell him about the pregnancy for her to get an abortion.
He admitted thinking about killing the teen — who was also his high school classmate — for a week.