People heard arguing, then gunfire. Oceanside police arrived to find Brandon Keiser dead on the sidewalk, the victim of multiple gunshot wounds.

That was shortly after 10 p.m. March 22, 2016, on South Freeman Street, south of Missouri Ave., near his condo and just blocks from the beach. He had been headed home from work and had just picked up a pizza.

Ten years later, the shooter’s identity remains unknown. Efforts to solve the slaying continue, and Oceanside police recently released a new piece of information: The gun used to kill Keiser is the same one used in a late-night San Marcos shooting three weeks earlier.

The investigation just got a big boost with the announcement that the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives has kicked in an additional $14,000 toward the reward for information. That brings the total reward up to $25,000 — all but $1,000 of it from ATF.

Assistant Special Agent in Charge Jose Medina from the ATF’s San Diego field office said his agency has worked on the Keiser case from the beginning, and when one of the agents saw news of the 10-year mark since the slaying, the agent asked to increase the reward. “That was approved all the way to the top,” Medina said.

Friends and family were shocked by the death of a Keiser, a passionate surfer who grew up in the San Pasqual Valley near Escondido and graduated from San Pasqual High School in 1999 before heading off to Cal Poly San Luis Obispo to earn a business degree.

Friends said he went to work in insurance — good pay but lacking fulfillment. They said he left to take a job as a driving instructor, making less money but enjoying himself more. He loved teaching, and it left him more time for surfing.

Keiser’s mother, Mary Keiser, told Fox 5 San Diego last week that her husband died seven weeks after their only child was fatally shot. “I figure that person is responsible for taking my son’s life and my husband’s life,” she told the TV station.

Oceanside police said Keiser had stopped and bought a pizza from Domino’s Pizza on Mission Avenue in downtown Oceanside, then drove the half-mile to his home. It was his last stop, and police are asking people who may have interacted with Keiser in or around the pizza shop or saw anything suspicious in the area to come forward.

“This one seems so out of the blue and random,” Oceanside Police Chief Taurino Valdovinos said.

Witnesses described the suspect vehicle as a small, dark-colored four-door sedan with a single red-light bar across the trunk connecting the two taillights, which police said is a description of a 2013-2016 Dodge Dart, or similar to it.

Few details of the San Marcos shooting have been shared. It occurred when a man was shot around 11 p.m. on Palm Road near the campus of Palomar College. The Sheriff’s Office said the victim was taken to a hospital with injuries not considered life-threatening. No arrests were made.

Valdovinos said the ballistics in the two cases were a match. “We believe that the same firearm was used in both cases,” he said.

The chief also said the department was “just ecstatic” when ATF added another $14,000 to the reward money. “If that encourages somebody to come forward that eventually leads to a suspect, that’s what we’ve wanted,” he said.

Medina pointed to the ATF’s “great relationship” with local, state and federal partners, and said “protecting the safety and well-being of the community from gun violence is our top priority.”

Oceanside police asked that anyone with information on the identity of the person or people involved in Keiser’s shooting death call the department’s investigation tip line at 760-435-4573. Anonymous tips can be left with Crime Stoppers at 888-580-8477. Anonymous email and text messages can be sent through sdcrimestoppers.org.