ROCKLEDGE, Fla. -

A Brevard County father accused of leaving a 9-month-old girl alone in a hot vehicle for hours now faces a charge of murder, officials announced Friday.

Steven Lillie, 31, who was initially arrested in June on charges of aggravated manslaughter in the death of his daughter, Anna Marie Lille, now faces felony third-degree murder charges.

Lillie found his daughter unresponsive in his pickup truck outside his workplace at 566 Barton Boulevard, according to police, who said Anna Marie had been left inside the closed truck for about four hours during the hottest time of the day.

Police said Lillie intended to drop his daughter off with a caregiver before going into work. Some type of disruption in Lillie's normal routine, however, caused him to forget that he had not dropped off the baby, according to police.

About four hours later, a family member asking about the girl prompted Lillie to run outside, officials said, where he found his daughter inside the truck.

In discussing the charges, the state attorney's office said the murder charge better fits the allegations.

"We had to carefully look, considering all statutes that were out there and all of the facts, and we determined that these were the best charges that fit all the facts and circumstances of this case," said Julia Lynch with the state attorney's office.

With initially being charged with aggravated manslaughter, police believed there was negligence involved in the death of Anna Marie. However, Lynch poured over evidence and interviews and believes this was all just a tragic accident, but Lillie still needs to be held accountable.

"We realize he didn't set out that day to harm or hurt his child, but if a person does the act, then they have to able to take the responsibility for that act," said Lynch.

Lillie is also being charged with voluntary manslaughter and leaving a child unattended. He bonded out of jail back in June and won't be rearrested for the new charges.

If convicted of the third-degree murder, he could face up to 20 years in prison, officials said.