The campaigner's fiancee Cynthia Kelley discovered the 47 year old's body at the bottom of the pool at their Rialto, California home on the morning of 17 June (12).
Police investigating the death immediately ruled out foul play and now their drowning suspicions have been confirmed by coroners, who have listed his cause of death as accidental drowning.
Toxicology results also showed King had been under the influence of a number of substances, including psychological drug PCP (phencyclidine), at the time of his passing.
King became infamous as the victim of a brutal beating by four Los Angeles police officers in 1991, sparking the notorious L.A. Riots.