A teen was convicted Tuesday in the brutal rape and murder of his high-school math teacher in Massachusetts. Philip Chism was found guilty of first-degree murder as well as charges of aggravated rape and armed robbery. Defense lawyers had argued that the 16-year-old suffered from a psychotic disorder when he killed Colleen Ritzer in 2013. The teen was just 14 at the time. The 24-year-old teacher was raped twice and her throat had been slit. Her body was later found in a wooded area near the school. Because he was a juvenile when the crime was committed, Chism will be sentenced to life in prison with the possibility of parole after 15 to 25 years.