d4vd is allegedly “not cooperating” with investigators amid the investigation into the death of Celeste Rivas Hernandez, a 15-year-old girl whose body was found in the singer’s car in September 2025.

A police source exclusively tells PEOPLE that the musician, 20 — born David Anthony Burke — is “not cooperating” with investigators, and has not cooperated from the beginning. The source also says that police have not yet interviewed the singer, and that there is still uncertainty surrounding which crimes d4vd and his accomplices may have allegedly committed.

The source adds that although d4vd has been identified as a suspect in Rivas’ death, the investigation remains ongoing. The source also notes that the Los Angeles medical examiner’s final cause-of-death determination and toxicology report are still pending, and no potential charges or arrest can be pursued until further findings are available.

“We are working to determine if her death was a murder or something else,” a police source says.

The source also shares that police still have not yet been able to determine when exactly Rivas died.

“Springtime is the closest we’ve come to determining the time of her death. Not before then,” the source says.

The LAPD, d4vd’s lawyer and a rep for the singer didn’t immediately respond when contacted by PEOPLE for comment earlier this week. The singer’s representative previously told NBC Los Angeles that his client was “fully cooperating” with authorities.

d4vd attends the 2023 Streamy Awards on August 27, 2023 in Los Angeles, California.Matt Winkelmeyer/Getty

On Sept. 8, Rivas was found dead in the trunk of d4vd’s impounded Tesla one day after her 15th birthday, while the musician was on tour in the U.S. The car was reported abandoned in the Hollywood Hills, and neighbors told NBC Los Angeles it had been there for about a month. Officers responded to the scene after others reported a foul odor coming from the vehicle.

Her body was identified by the Los Angeles County Medical Examiner, which listed her cause and manner of death as “deferred.”

The police source tells PEOPLE that investigators are treating the investigation as a homicide investigation, and shares that the girl’s body was decomposing when it was found inside a plastic bag.

Celeste Rivas Hernandez.GoFundMe

The Riverside County Sheriff’s Office previously said Rivas had been reported missing from Lake Elsinore, Calif., at least three times in 2024, according to the Los Angeles Times — and residents claimed the teen had run away from home before, though her last known whereabouts remain unclear.

LAPD Captain and Commanding Officer Scot M. Williams previously told PEOPLE that Rivas had been dead for “several weeks prior to her body being discovered.”

Also in September, investigators with the LAPD served a search warrant in connection with the death of Celeste Rivas Hernandez at a Hollywood Hills home where the singer had been staying, law enforcement sources previously told local KABC-TV and the Los Angeles Times.

A separate police source previously told PEOPLE that the perpetrator “most likely had help dismembering and disposing of the body.”