Slipknot bassist Paul Gray died of an accidental drug overdose, toxicology tests have revealed.

Gray had fatal levels of morphine and the morphine substitute fentanyl in his blood when his body was found in a hotel room in Des Moines last month.

Police said Gray had no prescription for either drug and that charges could be brought, according to the BBC.

Gray, 38, was one of the original members of Slipknot, who formed in the town in 1995.

Last month, the band's remaining members paid tribute to Gray, describing him as “an amazing person”.

(by Jason Gregory)