The Office Max on Geary and Arguello where Ryosuke Yoshioka was killed. (Photo by J.K. Yamamoto)

San Francisco homicide detectives investigating the death of Ryosuke Yoshioka, owner of Sushi Man on Bush Street, are still seeking witnesses.

Yoshioka, 59, who operated the popular sushi restaurant for 30 years, was stabbed to death on Jan. 7 around 2:45 p.m. in the upstairs parking garage of Office Max on Geary and Arguello in the Richmond District. He had gone there to buy paper.

Police identified the attacker as Peter C. Fong, 45, a Richmond District resident. Two witnesses who held Fong until police arrived said that he seemed incoherent.

Lt. Jim Spillane, one of the investigators on the case, said that Fong has given a statement to the police, but declined to reveal what Fong said.

Fong was scheduled to be arraigned for murder this week and has been assigned a lawyer from the Public Defender’s Office.

Asked if Fong had any previous run-ins with the police, Spillane said, “Not that I’m aware of.”

The inspector also said that nothing has been found to indicate that Fong knew Yoshioka, but the police haven’t definitely established that the attack was random.

Spillane emphasized that the police still want to talk to anyone who saw anything relevant to the case. “It was in the middle of the day in a crowded area. We’ve spoken with a lot of people, but there’s always a possibility of more people coming forward.”

Witnesses are asked to call Inspector Tom Newland at (415) 553-1291 or Inspector Brian Delahunty at (415) 553-1336. The anonymous tip line is (415) 575-4444.

Yoshioka is survived by his wife and 15-year-old son. A fund has been established for the family. Contributions can be made to the Ryosuke Yoshioka Memorial Fund, Account No. 2119185011, Wells Fargo Bank, 2055 Chestnut St., San Francisco, CA 94123.

Nathan Lau, a long-time customer and friend of Yoshioka, has established a memorial web page at http://chezannies.blogspot.com/2009/01/in-memoriam-ryosuke-yoshioka-sush.... He is asking for visitors to leave comments and for those who knew Yoshioka to share anecdotes or remembrances.