Authorities in the East Bay hope recently uncovered security video will help them track down the killer of a 30-year-old scientist who was gunned down last month in his quiet Oakland neighborhood.

The video shows Brian Bole, described by a friend as “peaceful, gentle and friendly,” encountering people minutes before the slaying, which occurred as he walked home around midnight on April 10 after a night out with friends, police said. The gunman opened fire on the usually quiet 3000 block of Richmond Avenue, and Bole, a former NASA contractor, died.

With no identified suspects in the case, detectives continue to seek a motive, and investigators turned to the public for help Thursday. Oakland police officials and the FBI released grainy photos of three “persons of interest” and a “vehicle of interest,” a 2003 to 2007 silver Honda Accord, captured on security cameras at businesses along the route he walked.

“We’ve done an intensive canvass of the area and reviewed hours and hours of surveillance footage,” the lead detective, Sgt. Leonel Sanchez, told reporters during a briefing at the slaying site.

He said video showed Bole “coming into contact” with several people as he walked from a Telegraph Avenue bar to the dimly-lit, tree-lined street where his body was found. Sanchez did not provide details of the encounters but said the people are considered persons of interest who may have information about the shooting.

“We know we can’t do this alone,” Oakland police Lt. Roland Holmgren added. “We’re asking anyone to come forward with any piece of information.”

Bole had “a lot of personal effects still on him,” Holmgren said, but investigators have not ruled out a robbery-gone-wrong as the motive.

Bole’s friends, family and co-workers are struggling with the loss of the brilliant data scientist, who most recently worked for Armus, a San Mateo health care software company.

“He was the most peaceful, gentle, and friendly person you could ever imagine,” Bole’s employer, Gyula Sziraczky, said Thursday.

At Armus for the past year, Bole crunched data for cardiologists in preventive health care programs. He considered it his “dream job,” several friends and co-workers said. Colleagues have been overcome with sorrow at the loss of Bole and the sight of his empty work chair, Sziraczky said.

“I wake up at night and my stomach hurts,” he said.

A native of Florida, Bole held a mathematics degree, and earned a doctorate in electrical engineering from Georgia Tech University. As a student, he began a NASA fellowship at Ames Research Center in Mountain View and soon fell in love with California and the outdoors, friends said.

The FBI, which assists Oakland in some homicide cases, added a $20,000 reward Thursday to the $10,000 already offered by the city of Oakland for information leading to the arrest of the killer.

Police said anyone with information about the case should call Oakland police at (510) 238-7950.

Evan Sernoffsky is a San Francisco Chronicle staff writer. Email: esernoffsky@sfchronicle.com Twitter: EvanSernoffsky