Drakeo the Ruler Murder Investigators Stalled, No One's Talking

Detectives working to find out who killed Drakeo the Ruler are fighting an uphill battle, finding it hard to get anyone who may have info on the suspect to come forward and talk ... TMZ has learned.

Law enforcement sources tell TMZ ... investigators are mostly relying on surveillance and cellphone footage to crack the case. As we reported, he was stabbed in the neck backstage at the Once Upon A Time in L.A. festival on Dec. 18.

Our sources say detectives attempting to chat with witnesses to the scuffle ... but they're not talking, which makes it hard/next to impossible to nab the culprits.

Detectives are starting to go another route -- looking to see if the Slim 400 murder might be connected to Drakeo the Ruler's demise.

As we reported, there's a lot of tension between gangs in the City of Angels as of late, so cops are well aware of the chance for retaliation.

Nothing's been made public to connect the Drakeo and Slim murders -- but our sources say cops aren't ruling it out.

Snoop Dogg, Ice Cube and 50 Cent were among the acts set to perform at the festival where Drakeo was killed ... Snoop posted a heartfelt message, saying, "My prayers go out to everyone affected by the tragedy. Please take care, love one another and stay safe y'all."

He ended with, "IM PRAYING FOR PEACE IN HIP HOP."