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SAN JOSE — They were two of Oakland’s newest firefighters, off the clock and enjoying a night out in San Jose with their academy mates when, suddenly and without warning, authorities say a man walked up and shot the pair in cold blood.

On Friday, the Oakland Fire Department was reeling from the seemingly senseless attack that killed Oakland native Jake P. Walter, 30, and wounded another firefighter. The group hailed from the vaunted 2-16 Academy class that graduated April 22 and were considered a promising boost to replenish the city’s overstretched fire brigade.

But the mourning was punctuated with the only good news amid the tragedy: The surviving victim, all of 26 years old, is listed in stable condition at Valley Medical Center in San Jose.

“We’re optimistic about his recovery,” interim Chief Darin White said during a Friday news conference.

An overnight manhunt led to the arrest of 27-year-old San Jose resident Oliver Juinio, according to San Jose police. Detectives believe that Juinio briskly walked up to a group of off-duty firefighters in front of a Taylor Street liquor store and shot the two men, according to a source familiar with the investigation.

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There is no known connection between the suspect and victims, and there was no lead-up to the gunfire, the source said.

Oakland Fire Department rank-and-file and brass spent the night in San Jose, standing vigil over their surviving colleague and rallying to support each other in the wake of Walter’s death.

“This is ongoing and unfolding. It was a long night for everybody, and will continue to be a long day,” said Oakland fire Deputy Chief Melinda Drayton.

White said he spoke with Walter’s parents Friday morning, and learned that the new firefighter took pride in serving his hometown.

“It was clear this is where he wanted to work,” he said. “This tragedy has left a somber cloud. … It’s got a domino effect throughout the department and beyond.”

The death of the Skyline High alum was another emotional blow to his fellow Titans, who lost an assistant football coach in June. Carlo Tateo, 31, was shot and killed in San Francisco while trying to stop a fight.

As a senior in 2006, Walter, the baseball team’s captain, led the Titans to a section title. School Athletic Director Don Ardissone remembers Walter as a humble leader who “did anything that was asked of him.”

He returned to his alma mater as an assistant coach for a few seasons, stepping away last year to go into the fire academy, Ardissone said.

“He always wanted to be a firefighter. He wanted it so badly he hung in there and hung in there to achieve that goal. Things were sailing along well for him,” Ardissone said. “These kids are going to miss out on having that kind of a role model. It just makes me sick.”

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Grief counselors are expected to be on the campus Monday, the first day of the fall semester.

White said that while firefighters are trained to routinely respond to traumatic situations and willfully walk into danger, the department could not steel itself from the shock of Walter’s death.

“We don’t think about chance encounters off duty that could lead to a similar outcome,” White said. “This totally caught us off guard.”

Oakland Mayor Libby Schaaf extended condolences to the victims on behalf of the city. She also thanked the victims’ colleagues for rendering aid to them immediately after the shooting, as well as responding San Jose police and fire personnel.

“Our thoughts and prayers go out to the families who are grieving from last night’s terrible tragedy,” Schaaf said in a statement. “We grieve for our colleague and wish the injured firefighter a speedy recovery.”

San Jose police were called to the 300 block of East Taylor Street at 9:37 p.m. Thursday outside the Gordon Biersch brewery for a report of a shooting. They found two men suffering from gunshot wounds.

The two victims were with three fellow academy classmates, attending the Taylor Street Night Market at the brewery, where a food-and-music event was being held to honor the seventh anniversary of Cukui, an independent South Bay clothing company.

“They were at an event, exiting the establishment,” Drayton said, calling the attack “a random act of violence without provocation.”

Neither of the victims was dressed in any clothing with OFD insignia or any other apparel that would indicate they were firefighters, Drayton said. After they were shot, their colleagues immediately worked to render CPR and first aid.

In the hours after the shooting, fire engines lined South Bay freeway overpasses overnight as the slain firefighter was taken, presumably to the Santa Clara County Medical Examiner-Coroner’s Office. A similar sight occurred Friday afternoon, as Walter’s body was taken along Interstate 880 back home to Oakland.

The shooter ran from the scene, prompting the shutdown of Taylor Street between Seventh and Ninth streets as a helicopter circled the area, occasionally issuing commands for the suspect to surrender or risk being bitten by police dogs. Within about an hour, officers located Juinio hiding in a home near 10th and Taylor streets and took him into custody.

As of Friday afternoon, police were still searching for the gun used in the shooting. No other suspects were being sought.

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Juinio was booked into the Santa Clara County Main Jail, where he is being held without bail. He has a handful of criminal cases, according to county court records, primarily involving property crimes, and made news headlines in 2010 when he was arrested in connection with a Saratoga burglary.

His uncle, Roberto Ouano, with whom Juinio lived when he was a teenager, voiced surprise at the news that his nephew was a suspect.

“I hope it’s not him. It surprises me. He was like a normal person,” Ouano said.

He last saw his nephew about two months ago at a relative’s birthday party.

“He didn’t look like he was having a problem,” Ouano said, describing him as a “happy-go-lucky guy.”

Anyone with information about the incident can contact San Jose police homicide Detective Sgt. John Barg or Detective Wayne Smith at 408-277-5283 or leave a tip with Silicon Valley Crime Stoppers at 408-947-STOP (7867) or svcrimestoppers.org. Tipsters may be eligible for a cash reward.

TO HELP

Anyone wishing to make monetary donations in support of the fallen and injured Oakland firefighters can do so by sending a check made out to the Friends of Oakland Fire, or the Oakland Firefighters’ Local 55 Charity Fund. Donations to either organization can be sent to 150 Frank H. Ogawa Plaza, 3rd floor, Oakland, CA 94612.