Prosecutors have not released the name of the 17-year-old because he is currently being charged as a juvenile. He was 16 when he allegedly killed Hill on March 21.
Brazoria County District Attorney Jeri Yenne said her office will move to have the teenager tried as an adult. He was being held in the youth detention center Wednesday.
Hill was found dead in her home in a gated community, her autopsy report said she was both strangled and stabbed. She was pregnant with twins at the time of the murder, investigators said that DNA testing confirmed the teenage suspect was the father.
Yenne said little about the teenager's alleged motive.
"It is important to us that this 17-year-old male be held accountable and the family of Arrijana Hill receive justice. She was brutally murdered," Yenne said.
Both Hill and her alleged killer attended Glenda Dawson High School at the time of her death. A spokeswoman for the Pasadena school district said the teenager transferred to Pasadena Memorial six days later.
The suspect was arrested at school this week.
Christopher Hartwell, the pastor of Crossroads Community Church, said that Hill was a "praise dancer" and participated in many youth activities, including track and volleyball. Sharee Shepherd, one of her coaches, said she was a "hard worker."
"She was sweet, very friendly," Shepherd added.