A gunman was arrested in Nevada Friday evening after killing a family member in Oakland earlier in the day, then heading to San Francisco and killing another relative in the Bayview district hours later, authorities said.

Stefon Jefferson, 43, was taken into custody Friday night in Douglas County, Nev., according to the San Francisco Police Department.

Jefferson was found after authorities released photos of him and his vehicle, a black Toyota Camry with the California license plate 7WVY390.

In San Francisco’s Bayview district, Jefferson is believed to have opened fire about 1:30 p.m. on the 2600 block of Arelious Walker Drive near the new Alice Griffith public housing development. Laron Davis, 49, of San Francisco was killed in the shooting, according to the San Francisco medical examiner.

Hours earlier in Oakland, Marcus Jackson was shot and killed outside his home on the 4100 block of Market Street, police and witnesses said. He was pronounced dead at the scene.

An Oakland officer said both victims were relatives of the suspect.

Jackson’s neighbors, Calvin Douglas and Deshaon Douglas, said they were in their kitchen when they heard up to six gunshots. They immediately dropped to the floor and called 911, they said.

Jackson lived with his adult son in one unit of his property, while the suspect and his mother live in another unit on the same property, they said.

“Marcus was coming to check on his son, and then that happened,” Calvin Douglas said. “Something happened last night between the guy that did the killing and (Marcus Jackson’s) son, and Marcus was coming to check on his son and the guy was waiting for him.”

When Calvin Douglas looked out his window, he said, he saw the mother of the suspect standing over Jackson’s bloodied body.

“She laid there with his body. She told the police, ‘My son did this, and that is my nephew,’” Calvin Douglas said.

Deshaon Douglas said her 30-year-old daughter saw Jefferson outside waving his gun around after the shooting.

“He lived there with his mom,” Deshaon Douglas said. “But apparently he has some mental health issues. ... Marcus was a good man that did not deserve this at all. He was trying to protect his son.”

On Friday night, police tape was wrapped around the driveway of a multiunit residential building where Jackson was killed. An officer in a car parked outside the building said he was keeping watch over the home because of the family’s fear that Jefferson would return.

UC Berkeley police were also on the hunt for a suspect in a fatal shooting at People’s Park on Friday afternoon.

Lt. Bill Kasiske said the department is aware of the Oakland and San Francisco shootings and has not “confirmed or eliminated” the possibility of a connection to the Berkeley slaying.

The Berkeley shooting occurred at 3:30 p.m. at the park, which is part of UC Berkeley’s property. Police were looking for the suspect who fled the scene in a car. Police declined to release details about the car. The victim, whose identity was not immediately available, was taken to a hospital, where he later died.

“We have some leads, but we’re not releasing the information yet,” Kasiske said.

Sarah Ravani, Evan Sernoffsky and Trisha Thadani are San Francisco Chronicle staff writers. Email: sravani@sfchronicle.com; esernoffsky@sfchronicle.com, tthadani@sfchronicle.com Twitter: @SarRavani, @EvanSernoffsky, @TrishaThadani