Roger Reece Kibbe — one of America’s most notorious serial killers — was found dead in the prison cell he shared with another inmate … and authorities say it could be homicide.

Kibbe, infamously known as the ‘I-5 Strangler,’ was found lying unresponsive in his California state prison cell around 12:40 AM Sunday … and law enforcement says his cellmate, Jason Budrow, was standing next to the body.

Kibbe’s body was transported to the prison’s health care facility, but life-saving measures were unsuccessful and by 1:23 AM he was pronounced dead … according to authorities, who say they are launching a homicide investigation.

81-year-old Kibbe was serving multiple life sentences at Mule Creek State Prison after pleading guilty to raping and murdering 7 people, with some of the killings dating as far back as the 1970s.

Bobby Shmurda just ripped a page out of his pal Rowdy Rebel‘s playbook … copping a $100k chain that glows in the dark.

Rowdy Rebel hit up celeb jeweler Eric Da Jeweler to create something special that he could gift Bobby to celebrate finally getting out of prison. Eric came up with this beauty … a pendant and chain encrusted with a whopping 75 carats of emerald-cut diamonds!!!

Talk about your name in lights … all that ice spells out SHMURDA, with a glow-in-the-dark border outlining it.

We’re told Eric gave it to Bobby right after he got out last week — ’cause, as everybody knows, the fresh-outta-prison starter pack must include crazy bling.

As you might remember … Rowdy Rebel’s demon chain was waiting for him when he got out back in December. Eric was also the brains behind that chain … which featured 50 carats of diamonds.