AURORA, Colo. -- The mysterious case of two children found dead in their beds last August may finally yield an arrest.

Police have issued an arrest warrant for the children's father, Robert Raffie Henderson.

The 29-year-old Aurora man faces two counts of knowing and reckless child abuse resulting in death and two counts of second-degree assault for drugging them, a spokesman for the district attorney said.

An overdose of a generic cough and cold syrup killed 5-year-old Robert Killian and 4-year-old Rhapsody Henderson, according to the coroner's report.

The pair apparently took a large dose of a store-brand liquid cold medicine before they took their afternoon naps on Aug. 8. They never woke up.

The coroner's report said that the children died of a combination of pseudoephedrine, acetaminophen and dextromethorphan, ingredients found in many over-the-counter cold cough syrups, including the Smart Choice Night Time Cold Medication which was found in their home.

The ingredients can be deadly in large quantities, but doctors said it likely would take several times the recommended dose to kill an otherwise healthy child, 7NEWS reported.

Robert Raffie Henderson became the focus of the police investigation after he changed the story he told investigators.

Henderson said that the children were not feeling well that morning. He said that at lunchtime, he fixed the pair peanut butter and jelly sandwiches, they watched a little television, then they all went back to bed.

When Henderson went to work that afternoon, his wife, Fay Henderson, came home and was told not to bother them because they were sleeping. Later in the evening, when relatives dropped by and wondered why the children were still asleep, a young cousin found them dead in their separate beds.

Investigators said that the boy appeared to be on an unnatural position when he was found laying on his back with his "right arm appearing to be propped up" and "creamy colored froth around the nose area." Officers believe the boy did not die in bed and had been moved after he had died.

They confronted Henderson about it and even though he had repeatedly denied giving the children anything for their illness, he then admitted that he gave the children adult cough syrup, according to the affidavit.

Smart Choice Night Time Cold Medicine is clearly labeled as an adult medication and specifically states that it should not be given to children.

According to the affidavit, it was quite obvious that something was wrong with the children. 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.

The cold medicine was found in the closet, in a pink basket about 50 inches from the floor. The cap was securely on the bottle and it was child-resistant.

Henderson has not been arrested and is expected to turn himself in later today.

He has been described by his family and friends as a very good father.