Serial killer and rapist Richard Ramirez, a self-proclaimed believer in Satan, reportedly turned bright green the day before he died due to liver failure.

The 53-year-old had been on death row for 24 years, since being convicted of 13 murders and 11 sexual assaults, among other crimes, in 1989.

A New York Post report quotes sources saying "he was the colour green" and looked like the Jolly Green Giant, hours before his death at the Martin General Hospital in California.

"He looked like a green highlighter pen. He was sitting up in his bed doing stretches," the source continued.

It is understood this was not the first time Ramirez had been admitted for health issues.

The man dubbed The Night Stalker had a murderous career, shooting and raping his victims through the 1980s. Bizarrely, his popularity rose after he revealed his love for and devotion to Satanism. In fact, he became something of a cult figure for several women, one of whom married him while he was imprisoned in San Quentin.

The first time Ramirez was produced in court he displayed a tattoo of a pentagram on his palm and yelled "Hail Satan". And, after he was convicted of his crimes, he flashed the two-fingered "devil sign" to photographers and muttered "Evil".

In one of his interviews, speaking from prison to 3TV reporter Mike Wattkiss, Ramirez admitted to studying Satanism. But when asked if he was a "devil worshipper" he said "No comment".

He would only say, about Satanism, that it was "undefined wisdom instead of hypocritical self deceit. It is power without charity. A Satanist admits to be an evil. Yes I am evil."

Check out a video of Richard Ramirez, the Night Stalker, admitting he is "evil"

[Video Courtesy: YouTube/Bobby Victor]