The California serial killer who died in prison earlier this month succumbed to a form of cancer.

Richard Ramirez, who is known as the Night Stalker, died of complications from B-cell lymphoma, a cancer of the lymphatic system, according to the Marin County coroner's office. It listed other "significant conditions" including chronic substance abuse and hepatitis C, which is often spread by the use of intravenous drugs.

The drug abuse predated Ramirez's time in prison, said Lt. Keith Boyd, assistant chief deputy coroner.

"That's chronic drug use prior to incarceration," he said. "There's nothing to support any kind of drug use while incarcerated."

The drug use was the likely cause of the hepatitis C infection, Boyd said.

"It's likely something that he has been dealing with for years," Boyd said. "It's killing your liver."

Ramirez died June 7 at age 53 at a hospital where he had been taken for treatment of liver failure.

Lt. Sam Robinson, a prison spokesman, said he could not immediately comment.

The so-called Night Stalker terrorized Southern California in the mid-1980s.

Ramirez had been on death row at San Quentin State Prison since he was convicted in 1989 of 13 murders in 1984 and 1985. He also was convicted of rape, sodomy, oral copulation, burglary and attempted murder. Executions have been on hold for years, however, because of ongoing legal challenges.

Ramirez was a self-proclaimed Satanist whose trial produced gruesome details about his mutilation of his victims.

He was nicknamed the Night Stalker by the media because residents were warned to lock their doors and windows as the killings peaked during the hot summer of 1985. The killer had been entering homes through unlocked windows and doors. He then killed his victims with a gun or knife, burglarized the homes and sexually assaulted his female victims.

Based on reporting by The Associated Press.

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