HULL, Mass. -- Police have released the tape of the 911 call made by the parents of a 4-year-old girl who died of a prescription drug overdose before Christmas.

Both parents, Michael Riley, 34, and Caroline Riley, 32, have been arrested and charged in connection with Rebecca Riley's death.

NewsCenter 5's Shiba Russell reported that the call was made after the girl's parents realized she was dead.

Prosecutors said the child was a like a walking zombie before her death on Dec. 13, 2006. They said she was lethargic, vomiting and short of breath for at least five days before her death, but no one took her to the doctor. They said instead of taking the girl to the hospital, her parents gave her more pills.

According to the tape, Michael Riley called a 911 dispatcher from his home in Hull saying, "Can I get an ambulance to 90 Lynn Ave? My daughter passed away in the night."

He claimed his daughter died after choking on her own vomit. Now, two months later, he and his wife have been charged with the slow and deliberate overdose of their youngest child.

"This little girl was given repeated overdoses of Clonidine used to knock her out and essentially to shut her up," state prosecutor Frank Middleton said.

When police entered the couple's bedroom they found Riley on the floor, covered in her own bodily fluids.

"This little girl's lungs filled with liquid and she gasped and choked and vomited what she could out of her airways until she couldn't do it anymore. Until her body couldn't fight anymore, and she died," Middleton said.

The autopsy revealed that Rebecca Riley died of a lethal combination of drugs. The Rileys are accused of giving her too much Clonidine, a drug used to treat hyperactivity. When she was just 2 1/2 years old, a Boston psychiatrist diagnosed her with bi-polar disorder.

More charges could follow. The Plymouth district attorney's office said Rebecca's psychiatrist at Tufts New England Medical Center and the pharmacy that doled out the medications, are all part of the investigation. The state's Board of Registration for Medicine is also investigating.

Michael Riley was indicted in September 2005 of attempted rape of a girl under 14, four counts of indecent assault and battery on a child, and giving pornography to a child. He was scheduled to stand trial in May. He was free on $25,000 bail posted by his wife.