A garbage collector on death row since 2016 for the "Grim Sleeper" serial killings that terrorized southern Los Angeles for decades has died in prison.

Lonnie David Franklin, 67, who murdered nine women and a 15-year-old girl between 1985 and 2007, was found unresponsive in his cell Saturday evening. He was pronounced dead around 20 minutes later.

"His cause of death is pending the results of an autopsy; however, there were no signs of trauma," prison officials said in a statement.

Franklin stalked the streets of South Los Angeles at a time when an epidemic of crack cocaine plagued the neighbourhood.

Several of his victims were prostitutes and drug addicts whom he shot or strangled, dumping their bodies in alleyways or trash bins. He raped some before killing them. Franklin earned the moniker "Grim Sleeper" because of a 13-year gap in the murders.

Prosecutors at his murder trial said Franklin took advantage of some of his victims' addiction to crack, luring them to his backyard camper with money and drugs before killing them.

They voiced suspicions that Franklin may have been behind dozens more murders. Investigators searching his home found nearly 200 pictures and videos of women, many of whom have not been identified.

He died at San Quentin State Prison, outside San Francisco. California reinstated capital punishment in 1978. Thirteen death row inmates have been executed in the state since then, with far more dying of natural causes in prison.

Some 727 people remain on death row in California, but Governor Gavin Newsom imposed a moratorium on carrying out executions last year.

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