SAN ANTONIO (AP) — An 18-year-old has pleaded guilty to murder after authorities say he used a baseball bat to kill a retired teacher who looked after him.

Associated Press reports Isaac Nathaniel Rodriguez was 16 when he was charged as an adult in 2012 in the slaying of 63-year-old Adriana Carrillo Terry. He'll be sentenced next month.

Terry's relatives say she had considered herself like a grandmother to Rodriguez since his mother had been dating Terry's son. They say she let him live with her.

Terry used to work at the San Antonio Independent School District and recently accepted a job at a charter school.

She was planning to move and Rodriguez was set to move in with his mother, which police say may have caused him to attack Terry.