Patrick Sullivan was arrested at the scene minutes after allegedly stabbing 40-year-old William Quinn, of San Francisco, at about 1:50 a.m. inside the Cadillac Market at 499 Eddy St., according to police.
Police spokesman Sgt. Wilfred Williams said homicide investigators believe a verbal argument between the two men began outside the store and continued inside. It was not immediately known what the argument was about.
Irfan Ali, the owner of the market, said today that one of his employees, who was working behind the counter at the time, told him that a man walked in and asked the employee to call 911.
A second man, apparently Quinn, followed the man inside the store, according to Ali.
Ali said the first man then pulled a knife on Quinn and stabbed him.
Ali said he had "no idea" why the stabbing occurred. He added that police responded quickly to make the arrest and were examining surveillance video from the store.