A Montgomery County man so severely sexually assaulted his infant daughter last weekend that she died from the injuries, authorities said Tuesday.

Austin Stevens, 29, was arrested Sunday and charged with involuntary deviant sexual intercourse, rape of a child, aggravated assault, and related offenses in the death of his 10-month-old daughter, Zara.

"It’s hard to imagine how this child’s death could be more traumatic,” District Attorney Kevin Steele said at a news conference announcing the charges. "Sexual assault on an infant is heinous, and the inaction by her father led directly to her death.”

Stevens remained in custody Tuesday, unable to post $1 million bail. He is not charged with murder, prosecutors said, because the ruling on the cause and manner of the baby‘s death is pending the results of forensic tests.

Police were called Saturday to Stevens’ home in Collegeville, where they found the infant unresponsive, according to the affidavit of probable cause for his arrest. A medic later declared the child dead after unsuccessful attempts to revive her.

Stevens, who works as an assistant coach for the Lower Providence Warriors youth football team, had a custody agreement with the baby’s mother, Steele said. Their arrangement, he said, was not mandated by a judge and had been “amicable.”

At the time of the child’s death, Stevens had sole custody under the terms of an agreement with her mother, prosecutors said.

In an interview with county detectives, Stevens said he had left the baby in the bathtub briefly to go into the kitchen, and suddenly heard a bang, according to the affidavit. When he went to investigate the noise, Stevens said the infant wouldn‘t move or wake up, and couldn’t lift her head. He then called 911.

Detectives searched Stevens’ phone and found that he Googled “how to give CPR to a baby” and “how do you know if a [baby] is dead” before calling police, the affidavit said.

In a second interview, Stevens admitted to conducting those searches while “panicked.” He also spent time on social media before calling police about his daughter. The conversations, Steele said, were unrelated to his daughter‘s injury.

An autopsy later revealed that the baby had injuries consistent with sexual assault, and had suffered blunt-force trauma to her head, authorities said.

Stevens is scheduled to appear in front of a district judge for a preliminary hearing Oct. 14. There was no indication Tuesday that he had hired an attorney.