Philip Chism's phone was later broken. A search warrant police obtained Monday allows a forensic examination to determine if he used it during the alleged attack on Colleen Ritzer, 24, the Boston Globe reported.
Ritzer's body was found in a wooded area next to Danvers High School in October. Chism, 14, has been charged as an adult and allegedly attacked her in a bathroom at the school.
In an affidavit filed last week to support the application for a warrant, State Police Detective Steven J. Buccheri said investigators are also looking for evidence of advance planning, like Internet searches or notes made by Chism.
Chism, 14, allegedly admitted the attack to police but has pleaded not guilty to first-degree murder and rape.