With two pistols strapped to his braces and carrying a bag packed with hundreds of bullets, Gian Luigi Ferri coolly took the lift up to the 34th floor of a sleek glass and granite building in the city's financial district and began shooting.
After prowling through five floors while office workers dived under their desks for cover, Ferri turned his gun on himself, committing suicide in a stairwell as police officers approached. 'When he saw the officers he put the gun under his chin and fired one shot,' Frank Jordan, the mayor of San Francisco, told reporters. Ferri had shot dead eight people and injured six others.
Ferri was the president of a small mortgage and estate agency in Woodland Hills, a suburb of north Los Angeles, 400 miles to the south. Although his exact motives were unclear last night, he was known to have been involved in litigation with Pettit & Martin, a large Californian law firm with offices on the 34th floor of the 48-storey building which appeared to be the target of his attack. One of the firm's partners and one of its employees were among the dead.
There were unconfirmed reports that Ferri believed he was cheated in a land deal, in which he stood to lose dollars 300,000 ( pounds 199,000). Property prices in California have crashed in recent years, as a result of a lingering slump and cutbacks in the region's defence industry. There were also unsubstantiated reports that a suicide note and a hit list were found on his body.
Nancy Asbill, an attorney at Pettit & Martin, was in the washroom when he started shooting.
'We heard the fire alarm,' said Ms Asbill, who was visibly shaken. 'We thought it was a fire drill. Then we saw the bullet holes and smelled the smoke. We ran out.'
The gunfire, which began at around 3pm on Thursday, lasted for more than an hour, causing chaos in the streets outside. Inside, warnings were broadcast on the intercom urging workers to stay in their office suites and lock the doors. The shooting caused chaos in the busy district; underground and cable car routes running through the area were temporarily shut down and emergency vehicles surrounded the building.
Incidents such as this are not uncommon in a country where powerful weaponry is cheap and in abundant supply. The worst in the United States happened in October 1991 when 23 people were shot dead in a restaurant in Texas. It surpassed the 1984 slaughter at a Southern California fast-food restaurant that killed 21, and a massacre in Montreal, Canada, in which 14 were killed and a dozen wounded.
But middle-aged businessmen do not fit the usual assailant's profile. Mr Jordan told television viewers yesterday: 'No one was suspicious because he was wearing a business suit and a shirt and tie.'
Neighbours of Ferri yesterday described him as quiet and friendly person, who very rarely talked about himself. His dry cleaner told reporters that he did not seem unstable - he did not even get upset when the laundry lost one of his shirts.