Victim Corriann Cervantes was found dead at 4:10 a.m. on Feb. 8 in a Houston apartment.
Jose E. Reyes, 17, was arrested Sunday, and a 16-year-old boy was arrested Monday. Both have been charged with capital murder.
They are accused of kidnapping the girl before sexually abusing her, stabbing her and beating her to death.
The girl was found with a crucifix carved into her stomach, the Houston Chronicle reported.
Before the killing, Reyes had told the 16-year-old that he had sold his soul to the devil, and the juvenile had asked if he could do it, too, officials allege.
"And if they ended up killing this teenager, it would also allow the 16-year-old to also sell his soul to the devil," Assistant Harris County District Attorney John Jordan said.
Reyes is being held in the Harris County jail without bail, and the 16-year-old is in the county juvenile courthouse.