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An Altadena man has been charged with killing his mother and uncle while one of the victims was on a Zoom call last week, officials announced Monday.

Robert Anderson Cotton, 32, faces two counts of murder with an allegation of using a knife as a deadly and dangerous weapon, according to the Los Angeles County District Attorney’s Office.

On March 22, Cotton allegedly fatally stabbed his mother Carol Brown, 67, and his uncle Kenneth Preston, 69, in the house they all shared along the 3000 block of North Marengo Avenue.

Brown was apparently on a Zoom call with a colleague when the attack started. The witness on the virtual call saw the attack on both victims and called 911.

Preston was dragged out of the house while Brown was still on the Zoom call. The suspect allegedly then went inside and attacked Brown, Los Angeles County Sheriff’s Department officials said at the time

Preston was found dead on the home’s driveway, while Brown was found dead inside.

Though Cotton was not home when investigators arrived at the scene, they noticed a vehicle was missing.

The suspect then returned to the residence in the victim’s vehicle and was taken into custody.

It is unclear what led up to the double homicide and authorities have not released a possible motive.

“This is a horrific case in which the mother’s work colleagues witnessed part of the attack while on a Zoom call and called the authorities,” District Attorney George Gascón said in a news release.

Cotton was scheduled to be arraigned Monday, but the arraignment was continued to April 5, officials said.

The case is being investigated by the Los Angeles County Sheriff’s Department.