Raleigh, N.C. — A Wake County jury tasked with deciding whether a Raleigh man should be sentenced to death for killing his 10-month-old stepdaughter told a Superior Court judge Monday that they can't reach a unanimous decision.

The six men and six women spent most of the afternoon deliberating after prosecutors and defense attorneys for Joshua Andrew Stepp argued their reasons for and against the death penalty Monday morning.

Stepp, 28, was convicted last Thursday of first-degree murder and sex offense of a child in the Nov. 8, 2009, beating death of Cheyenne Yarley.

By 4:30 p.m., the jury decided on a sentence of life in prison, but Superior Court Judge Osmond Smith ordered jurors to continue deliberating after finding that at least one indicated that she voted for the death penalty.

The sentencing decision must be unanimous. If the jury becomes deadlocked, Smith would have to declare a sentencing mistrial, meaning Stepp would automatically be sentenced to life in prison without the possibility of parole.

Prosecutors asked that the judge hold off on declaring a mistrial, saying jurors hadn't deliberated the case long enough.

"This is the question of life and death, and three-and-a-half hours isn't a significant length of time for this case," Wake County Assistant District Attorney Adam Moyers said.

The state contends that Stepp attempted to rape Cheyenne, beat her to death and then lied to her mother, emergency responders and police about what happened.

"He nearly tore her to pieces," Moyers said Monday morning during closing argument in the sentencing phase of Stepp's trial.

Stepp, who testified on his own behalf, admitted to killing Cheyenne, although he said he didn't know why he did. He has denied the accusations of sexual assault.

Defense attorneys argued that his actions amounted to second-degree murder, because he was using prescription painkillers and alcohol to treat undiagnosed post-traumatic stress disorder resulting from his tour of duty in Iraq, where he saw members of his platoon killed by a roadside bomb.

"There's no excusing it. There's no one in this room who wishes it didn't happen, but there is an explanation for what happened," defense attorney Tommy Manning told jurors.

Manning noted that witnesses testified that Stepp has been a good father to his older daughter, was a good soldier and a trustworthy employee.

Moyers, however, said Cheyenne's murder was so heinous that it was like a black hole.

"He has forfeited his right to live," he said of Stepp.