AUBURNDALE, Fla. (AP) — A central Florida man is charged in the death of his 11-month-old stepson.

The Polk County Sheriff’s Office says Edwin Cruz Vargas of Auburndale became frustrated with Josiah Figueroa on Saturday and shook the baby.

According to an affidavit, Vargas told detectives that he tried feeding Josiah and hit the baby on the back when he became unresponsive. The affidavit says Vargas called 911 and slapped and punched the baby while doing CPR to try to wake him up.

An autopsy Monday found that Josiah suffered a broken back, among other injuries. The medical examiner said the cause of death was blunt force injury and ruled the death a homicide.

Vargas is charged with aggravated child abuse and negligent manslaughter. It wasn’t clear if he had an attorney.

Copyright 2012 The Associated Press.