Paul Huebl says he has turned over evidence to the FBI that shows the 48-year-old singer was killed over a drug debt in February 2012, reported Daily Mail.

Huebel claims that Houston drowned in her bathtub at the Beverley Hilton hotel after taking a cocktail of cocaine, marijuana and several legal drugs.

He believes that the troubled star was targeted by several "high powered drug dealers who sent thugs to collect a huge debt she owed for drugs".

The singer reportedly owed USD 1.5 million to dealers.

He said that Houston had previously been subjected to harassment by dealers trying to collect on her debt and he obtained surveillance video that shows two unknown men who repeatedly went to the Beverly Hilton and integrated themselves into Houston's entourage.

The private investigator claims these are the men who slipped into Houston's hotel room and killed her.

"Whitney's body shows classic defense wounds that would have occurred while she was battling for her life," said Heubl, a former Chicago police officer who became an actor after he retired.

Huebl says he gave his evidence to the Chicago field office of the FBI in the hopes that the agency will open a criminal investigation.