AURORA, Colo. -- A father suspected of drugging his two young children with a lethal dose of over-the-counter cough syrup surrendered to police early Thursday, about two hours after telling a television station he had done nothing wrong.

Arapahoe County jail officials said Robert "Raffie" Henderson turned himself in shortly after midnight.

He had told a TV station in Denver that he didn't do anything wrong and that he wasn't going to run. He said that he is completely convinced that the cough syrup did not cause the children's death and that he and his wife have been researching certain viruses or bacteria that may have led to Killian and Rhapsody's death.

An arrest warrant accuses Henderson, 29, of two counts of child abuse resulting in death and two counts of second-degree assault. The four counts carry a combined penalty of 60 years in prison.

Authorities said Henderson, who worked nights as a taxi driver, gave 5-year-old Killian and 4-year-old Rhapsody cherry-flavored cough syrup after they complained of being sick the morning of Aug. 8.

When he left for work, he told his wife, Fay Henderson, not to disturb the children because they were still sleeping.

Hours later, a young cousin had gone into their bedrooms to wake up them up but when she couldn't stir them, she told Fay Henderson, who found them dead in their beds.

The label for the medicine, Smart Choice Nighttime Cold Medicine, warns parents not to give it to children younger than 12.

Coroner Michael Dobersen ruled the two children's deaths were caused by the combination of the four drugs contained in the medicine, including pseudoephedrine, acetaminophen and dextromethorphan.

According to the Rocky Mountain News, a forensic toxicologist calculated that at the time of the autopsy, Rhapsody and Killian each had a little more than half an ounce -- roughly 3½ teaspoons -- of the medication in their blood. The recommended adult dose is one ounce.

Henderson estimated he gave each child the equivalent eight teaspoons that morning, but Dr. Richard Dart, director of the Rocky Mountain Poison and Drug Center, said that even a dose of eight teaspoons would not likely have been enough to cause death.

Henderson initially denied giving the children medicine but three days after their deaths, he admitted to police that he gave them athe "dark red" liquid from a plastic container in the family's medicine basket which is stored in the closet.

Police said that they confronted Henderson when they noticed that Killian's body had been moved after his death and it was quite obvious that something was wrong with the children when they went to bed.

Both had been "purging some sort of fluid from their mouths and noses" and Rhapsody had "a large quantity of vomitous fluid that had come out and was on the bedding."

"The room was permeated with a distinct odor of vomit," the affidavit states.

Police said that the cap was securely on the Smart Choice Nighttime Cold Medicine bottle and it was child-resistant so the children could not have tampered with it themselves.

Fay Henderson told authorities her husband cared deeply for their children and was never abusive.

"He loved them very much and he always had an interest in what was going on with them," she told police, according to an arrest affidavit.

Prosecutors declined to address specifics about the case. It was unclear from the arrest affidavit whether police believed Henderson intentionally overdosed the children.

Henderson's preliminary hearing date is set for April 14 at 1:30pm at the Arapahoe County courthouse.