A double homicide investigation is underway after two people were found fatally stabbed in Altadena Monday afternoon, Los Angeles County Sheriff’s Department officials said.

The incident was reported about 2:45 p.m. along the 3000 block of North Marengo Avenue, officials said in a news release.

First responders said they found two victims, both of whom were Black and in their 60s, and declared them dead at the scene.

“When they arrived, they found an elderly male deceased in the driveway,” said Lt. Barry Hall of the Sheriff’s Department. “They checked inside of house and found an elderly female dead.”

Authorities say the woman was on a Zoom call with a colleague when the attack started. The virtual witness, who saw the attack on both the man and the woman, called 911.

“The person that the lady was still talking to on the Zoom with when the male was dragged out of the house, that alerted her and the suspect went inside and attacked her,” Hall said.

Both the man and woman sustained fatal stab wounds.

As detectives were investigating, they learned a vehicle was missing from the residence, the department said in a news release.

“Since we arrived here at the location, a person of interest returned to the scene in the victim’s vehicle and he has since been detained,” Hall said.

That person of interest, 32-year-old Robert Cotton, was later booked on suspicion of two counts of murder, the department said.

Cotton told authorities he lived at that residence. Neighbors told KTLA at the scene that the alleged suspect is related to the two victims.

The two victims were not a couple, the Los Angeles Times reported, and the nature of their relationship was not yet clear.

No further details about the incident have been released.

Anyone with information about the double homicide can call the Los Angeles County Sheriff’s Department’s homicide bureau at 323-890-5500. Those who wish to remain anonymous can call “Crime Stoppers” at 800-222-TIPS (8477).