Los Angeles police have opened a criminal investigation into Charlie Sheen, ET can confirm.

LAPD received a radio call on March 31 around 3:00 p.m. of a criminal investigation in which the 50-year-old actor is listed as a suspect, an LAPD spokesperson told ET on Wednesday. The Threat Management Unit -- which supervises investigations involving aggravated threats of violence and stalking, workplace violence, and all threats directed to Los Angeles city officials -- are now the lead detectives in the investigation.

As the case is ongoing, police have declined to release any specific names.

WATCH: Brett Rossi Says She's 'Scared' of Charlie Sheen After Filing Lawsuit

John C. Taylor, a lawyer representing Sheen’s ex-fiancée Scottine Ross, confirms to ET that the investigation involves Ross. The 26-year-old, who's better known as Brett Rossi, went to police regarding threats Sheen allegedly made and has also filed an emergency protective order against the actor, according to her lawyer.

“She takes this very seriously,” Taylor tells ET. “She intends to do everything she can to protect herself.”

The LAPD says they have not reached out to Sheen yet. ET has reached out to Sheen's rep, who had no comment.

WATCH: Charlie Sheen Claims Denise Richards Is Only Out for Money After She Files Lawsuit Alleging He's Not Providing for His Children

ET sat down with Rossi last December, after she filed a lawsuit against the Two and a Half Men star. Rossi, who was engaged to Sheen for nine months in 2014, is suing the actor for assault, battery, emotional distress, false imprisonment, and negligence, claiming he was “violent and abusive and uncontrollable” while abusing drugs and alcohol during the time the two were together.

“I’m tired of being scared,” Rossi told ET. “I’m scared of Charlie. I’m scared of the backlash.”

"I still think I miss what we could have had,” she added about their former relationship. “But at the end of the day, he's an addict. He only loves himself, he never loved me."

WATCH: Charlie Sheen's Nurse Ex-Girlfriend Says She Knew About His HIV Before Having Unprotected Sex With Him

Sheen’s lawyer, Marty Singer, has denied all of Rossi’s claims on his client’s behalf.

"Charlie Sheen intends to vigorously defend the lawsuit filed by Brett Rossi aka Scottine Ross. Numerous witnesses will dispute each and every claim made by Ms. Rossi," Singer said in a statement to ET. "We are confident that Mr. Sheen will prevail in this action and also will recover significant damages against her in connection with a pending arbitration that was commenced months ago."

WATCH: Brooke Mueller Confirms She and Kids Are HIV Negative After Charlie Sheen Interview

Sheen made headlines in November, when he confirmed that he was HIV-positive on the Today show.

"I have a responsibility now to better myself and to help a lot of other people," he told Today show co-host Matt Lauer. "And hopefully with what we're doing today, others may come forward and say, 'Thanks Charlie. Thanks for kicking the door open.'"

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