Joshua Stepp is charged with the 2009 death of Cheyenne Yarley.
Stepp was living in his south Raleigh apartment with his new wife and his toddler daughter from another relationship when his attorney said Stepp "lost it" after he could not get Cheyenne to stop crying.
He admitted pushing the child's face into the carpet creating a facial injury and causing head trauma. He also said he put toilet paper in her mouth when she continued to scream.
"You admit that you committed all those injuries to her," the prosecutor asked Stepp while he was on the stand Wednesday.
"I know I hurt her," Stepp replied. "I didn't know it was that bad. I just didn't realize!"
The state's aggressive cross-examination followed a morning of questions from Stepp's attorney - questions that made him choke up several times as he described his desire to be a good dad to Cheyenne and his own daughter.
Stepp told the jury about his problems finding work after returning from Iraq with posttraumatic stress disorder and learning his wife had an affair with a man in South Carolina.
But while he insisted he could never be angry enough to intentionally hurt or kill Cheyenne, the prosecutor asked if it was possible that he did hit her in the head and Stepp agreed.
"And it's possible you did rape and sexually assault her," the prosecutor stated.
"No, that never happened," Stepp said angrily.
"You said that you couldn't remember," the prosecutor added.
"Because I would get mad at wives, at girlfriends, throw a cell phone, but the last thing going through my mind would be sexual," Stepp said.
Stepp has said he does not recall specific times or actions related to the death of his stepdaughter because he was self-medicating his PTSD with alcohol and prescription pain killers, but said the girl sustained serious injuries to her genitalia when he tried to clean her after she soiled two diapers following the attack.