Detectives were continuing today to question a 48-year-old man arrested following a siege in central London.
The man is believed to have entered a building in busy Tottenham Court Road with gas canisters strapped to him and taken hostages.
Yesterday's incident sparked a major alert as both Goodge Street and Warren Street Tube stations were closed, businesses evacuated and one of the capital's busiest shopping streets shut.
Abby Baafi, 27, the head of training and operations at Advantage Training Services, a company which offers HGV courses, said the man, who called himself Michael Green, entered her offices and held four men hostage.
She said: "I recognised him because he was one of our previous customers, but he is not quite stable - mentally stable.
"He turned up, strapped up with gasoline cylinders, and threatened to blow up the office.
"He said he doesn't care about his life. He doesn't care about anything, he is going to blow up everybody.
"He was specifically looking for me but I said, 'My name's not Abby' and he let me go."
Ms Baafi said the man had failed the HGV training course and wanted his money back.
Sarah O'Meara, who works for the Huffington Post, said the news website's offices in nearby Capper Street were evacuated after the alert was raised by a woman who ran into the building.
She said: "A woman ran in off the street saying, 'There is a guy with a bomb and he is threatening to blow himself up' and that we needed to evacuate."
Witnesses also spoke of seeing office equipment including computer screens, computers and a filing cabinet be thrown from the windows of the building.
Police said the suspect, who is local, was removed from Shropshire House by officers who then carried out a search of the building.
Police received emergency calls at midday amid reports that the man was holding people captive inside the building, several floors above ground.
No hostages were inside the building when the man left, after negotiators had been sent to the scene.
Officers were also concerned that the suspect had explosives or flammable materials.
It is not known how the suspect arrived at the scene, whether by vehicle or on foot.
Scotland Yard was unable to go into details of whether witnesses had seen him walk to the building or whether they were looking for a vehicle possibly connected to him.