A 23-year-old transient has been identified as the alleged assailant in the fatal beatings of a wealthy couple who were found “brutally murdered” at the doorstep of their upscale La Verne-area home on the day after Christmas, law enforcement sources told KTLA on Wednesday.

Luke Matthew Fabela was believed to be the person responsible for the slayings, a source close to the investigation said.

Investigators found evidence linking Fabela to the Isom murders, and he has been in custody since Jan. 16, the source said.

Armie “Troy” and Shirley Isom died in what investigators called a “blitz attack” that occurred at or near the front door of their hillside home in the 300 block of Roughrider Road, in the unincorporated La Verne area of Los Angeles County.

Both victims sustained blunt-force trauma, and Shirley Isom had sharp-force trauma, Los Angeles County Sheriff’s Department Homicide Division Lt. Dave Coleman said at the time of the killings. Troy Isom was 89 and his wife was 74.

In the days following the attack, police released a sketch of a man seen in the neighborhood on the day the couple died.

He was described as a white or Hispanic man in his late 20s or early 30s and was wearing in “hiking attire.”

The man was seen outside the Isoms’ gate and then walking out of the neighborhood after the attack, witnesses said.

Fabela was the man allegedly seen by neighbors on the day of the attack, the source confirmed.

More information about Fabela and the case was expected to be released at a news conference on Wednesday.