SALEM, Mass. (AP) — A teenager who raped and killed his high school math teacher faces a sentence of up to life in prison when a judge hands out his punishment Friday.

Philip Chism was convicted in December in the 2013 death of Danvers High School teacher Colleen Ritzer. He was 14 when he followed her into a school bathroom, strangled her, stabbed her at least 16 times and raped her.

A judge in Salem Superior Court was expected to sentence Chism after hearing nine victim-impact statements from Ritzer’s family and friends. Many of them wore pink, her favorite color.

The 17-year-old Chism faces life on the murder charge but would be eligible for parole after 15 to 25 years. He also faces lengthy sentences on charges of aggravated rape and robbery. Prosecutors have asked that he stay in prison for at least 50 years.

At his trial, the defense admitted Chism killed Ritzer but said he was suffering from severe mental illness and wasn’t criminally responsible for his actions. A psychiatrist who testified for the defense said Chism, who had just moved to Massachusetts from Clarksville, Tennessee, was hearing voices and in the throes of a psychotic episode when he killed Ritzer.

Chism was convicted of raping the 24-year-old Ritzer inside the bathroom but was acquitted of a second rape, committed with a tree branch in woods near the school where Chism put her body. He was also convicted of armed robbery for stealing Ritzer’s credit cards and her underwear.