A California man has been charged with the murder of his elderly father-in-law, who police initially believed had died from natural causes.

Khanh Trong Tran, 71, was arrested on Friday, just days after his father-in-law, Sy Van Nguyen, 94, appeared to have died from natural causes in his Bay Area home, the Sonoma County Sheriff’s Department said.

Authorities were called to the residence on Monday, August 11, after Tran found his father-in-law unresponsive. The two men lived in different homes on the same property in Santa Rosa, about 55 miles north of San Francisco, SFGate reported.

At the time, the sheriff’s department said there were no signs of trauma or foul play.

However, days later, deputies “received evidence indicating the death was not natural, but instead an intentional killing.” Authorities have not shared any details about the new evidence they received.

Detectives quickly obtained a search warrant for the home, and later went searching for Tran, who was located early Saturday morning in a car about seven miles away.

Tran was taken into custody and booked into the Sonoma County Jail on suspicion of murder.

Neighbors said they were shocked to learn that Tran was suspected of killing his father-in-law.

“He seemed like a very nice guy, so it’s shocking he did that,” Lynn Burglund told ABC 7 News.

Other neighbors said they knew the 94-year-old victim, but that his son-in-law mostly kept to himself.

“He’s been a different neighbor than most of them around here. Keeps to himself, more or less, doesn’t want anyone on his property,” neighbor Don Pelletti said.

Another neighbor, who declined to be identified, said Tran was outdoorsy.

“He seemed nice enough, a little guy. When we talked about doing hiking things, he was exuberant about it,” the neighbor said.

Authorities have not shared Nguyen’s cause of death or any other details surrounding his death.