A Norristown man has been charged with third-degree murder after he shook his 6-week-old daughter to death, prosecutors said Thursday.

Craig Bayliss, 31, was arrested Wednesday in the death of Mackenna Bayliss, according to court records. He was denied bail and there was no indication he had hired an attorney.

Montgomery County District Attorney Kevin Steele said his office will “seek justice” for the infant and her family.

“A very vulnerable child — only a month and a half old — was left in the care of someone who should have protected her,” Steele said. “Instead, he shook the life out of baby Mackenna.”

Officers were called to a home in West Norriton Township on Feb. 22 for reports of a cardiac arrest, according to the affidavit of probable cause for Bayliss’ arrest. There, they found Mackenna unresponsive and without a pulse. The girl died about an hour later at Einstein Montgomery Hospital.

Her mother told detectives she was at a doctor’s appointment and had left Mackenna alone with Bayliss, the affidavit said. Bayliss had called her to tell her the girl had hit her head and suffered a nosebleed but was fine.

When the woman came home, she found Bayliss rocking the infant, who appeared gray and lifeless, according to the affidavit.

Bayliss, during multiple interviews with detectives, gave various versions of what happened inside the home, the affidavit said. Initially, he told investigators the girl had fallen out of bed and hit her head. He later recanted that statement, saying he had fallen asleep while holding the baby, and had awakened to find her facedown and unresponsive on the bed.

An autopsy conducted by the county coroner found that Mackenna had died from “inflicted head trauma,” likely from “vigorous movement of the head while relatively fixed in relation to the neck,” the affidavit said.