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A crime scene worker leaves a Colebrook Lane home where a shooting occurred on Sept. 7, 2022, in Dublin.

The booking photograph of Devin Williams Jr., 24, an Alameda County Sheriff's deputy, after he was arrested Sept. 7 on suspicion of murdering a Dublin couple in their home.

An Alameda County Sheriff’s deputy arrested for allegedly killing a Dublin couple by shooting them “execution style” was scheduled to be arraigned in court Friday as detectives continued to investigate the case.

Police say Devin Williams, Jr., 24, of Stockton, fatally shot Benison Tran, 57, and his wife, Maria Tran, 42, in their large stucco house on Colebrook Lane early Wednesday morning before fleeing in his car. Authorities suggested a prior relationship between Williams and the couple, but have not discussed a motive.

A nearly 12-hour search for the deputy ended when he called the Dublin Police Department — a contract agency of the Sheriff’s Office — late Wednesday morning and was talked into surrendering by Police Chief Garrett Holmes. Holmes kept Williams on the line until CHP officers could arrive and take him into custody 160 miles away in Coalinga (Fresno County).

The deputy, who worked for the Sheriff’s Office for a year, was booked into Santa Rita Jail in Dublin on suspicion of murder and burglary after he worked an overtime shift as a jail guard in the same facility Tuesday. As of Thursday, he was being held without bail.

Charges had yet to be filed against Williams but he was expected to be arraigned at 9 a.m. Friday at the East County Hall of Justice in Dublin.

Nearly two hours after ending his shift at the jail, Williams allegedly entered the home in the Dublin Ranch subdivison and “shot and killed a married couple in an execution style manner,” according to a police bulletin reviewed by The Chronicle. The couple’s child and a visting relative, who called 911 after the shooting, were also in the house but were not injured, police said.

The gun used in the killings, possibly the deputy’s service weapon, was discarded in the Altamont Pass area east of Dublin and Livermore, Williams allegedly told police. But as of Thursday afternoon, it had not been located, sheriff’s Lt. Ray Kelly told The Chronicle.

“We’re looking at all angles — and for a motive,” Kelly said. “There’s all kinds of speculation out there, people are talking. We want to make sure we’re getting everything right.”

A police bulletin issued before Williams’ arrest said they had identified him as the shooter in part because of “prior contacts at the residence.” Kelly said Thursday he was unaware of the nature of those contacts.

After graduating from the police academy at San Joaquin Delta College in Stockton, Williams went to work for the Stockton Police Department to get field training. He left after a year, Kelly said, after failing to successfully complete training, to work for Alameda County as a deputy in the courts and jails, positions that don’t require the field training.

Kelly said officers who haven’t completed their field training commonly take positions in courts or jails and complete their training later. Williams passed extensive background checks and psychological testing, Kelly said, with nothing raising red flags.

“Everything indicated he was a good candidate for law enforcement,” Kelly said at a Wednesday news conference.

Sheriff’s investigators have obtained search warrants allowing them to examine digital devices and communications, Kelly said, adding that he believes that data may be crucial in understanding the case.

“We know people communicate in today’s day and age via text, via email, via Facebook,” he said, “and all that needs to be analyzed. We think that will help us reach some kind of conclusion as to a motive.”

Michael Cabanatuan (he/him) is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan

Michael Cabanatuan is a general assignment and breaking news reporter who's covered everything from wildfires and sports fans to protests and COVID masking requirements. He's also written extensively about transportation and covered Contra Costa County for The Chronicle. He's ridden high-speed trains in Japan, walked in the Transbay Tube, been tear-gassed in Oakland and exposed to nude protesters in the Castro. Cabanatuan worked at the Paradise Post (long before anyone heard of the town), the former West County Times (in Richmond) and the Modesto Bee before joining The Chronicle. He is a two-time graduate of UC Berkeley.