JACKSONVILLE, Fla. -

A Navy man is now charged with murder in the killing of his girlfriend's 2-year-old son in 2010.

First Class Petty Officer Nicholas Rivet turned himself in to police Wednesday, walking in to the Jacksonville Sheriff's Office dressed in his Navy fatigues.

Rivet (booking photo, right), 35, is accused of throwing and beating Eddie Robb (pictured at bottom of story) to death. Police said he was upset that Robb had woken up his 3-year-old daughter in the middle of the night.

"Whatever that reason was, if the child was in there crying enough to go in there and pick up the child and slam him down or slam him against the wall, it's just unheard of. Unbelievable," said Lt. Rob Schoonover, of the Jacksonville Sheriff's Office.

According to the Medical Examiner, Robb died from blunt force trauma to his head. Doctors at UF Health Jacksonville say he suffered a brain bleed, a skull fracture, a blown pupil and was unresponsive when he arrived at the hospital on Jan. 25, 2010.

Investigators say the toddler and his mother, Brandi Robb, had been staying at Rivet's off-base military housing on Valley Forge Court, when Robb claims she heard a "thud" come from the upstairs bedroom where her son and Rivet's 3-year-old daughter had been sleeping.

When she went upstairs, she claims her boyfriend was coming out of the room and admitted her son had woken up his daughter and he was trying to get them both back to sleep.

As for why the arrest was made now, Schoonover said Brandi Robb passed a polygraph test. He said Robb and Rivet had previously given various accounts of what happened.

"His story has changed a couple of times over the past couple of years, and finally enough probable cause was gained to issue the warrant," Schoonover said.

Rivet is being held in the Duval County jail without bail. He made his first appearance in court Thursday morning. Rivet's next court date is set for June 13.

The Department of Children and Families said that more than half of all child abuse cases in Florida are at the hands of a mother's boyfriend.

"This happens all too frequently, so we urge parents first, use caution regarding who you allow around your children," said DCF's John Harrell. "Be cautious as to who you allow to be around your children, because national research shows that about 67 percent of child abuse cases involve perpetrators who are the boyfriends of the child's mother."

"The investigation has taken so long because you had Nicholas Rivet and the mother of Eddie Robb contradicting each other, going back and forth about who was at fault," said Lt. Rob Schoonover of the Jacksonville Sheriff's Office.

Channel 4 crime analyst Ken Jefferson said the case highlights the importance of screening people before you make them part of your permanent personal life.

"If you're going to consider someone to date or consider marrying, you might want to do a background check on them, a criminal background check on them," said Jefferson. "Check out their families, check out their past history, check everything you can about them."