People comfort each other outside the building
"There was somebody in a police uniform storming into the parliament," one witness said. "I was just outside the door of the parliament when he came in with a rifle, with several pistols and with what I think it was a hand grenade."
"I had been talking with one of the members of the [local] government. What I heard was she was killed. People were lying on the floor. It is really a nightmare," he added.
"It lasted around three minutes, almost like an execution," said Hanspeter Hausheer, a member of the assembly and a banker at UBS Warburg.
Police uniform
"As the man stormed up the stairs in a police uniform, we didn't think anything special was up. As the first shot was fired, I had the feeling it could be a blank because I didn't feel anything," he recalled afterwards.
Mr Hausheer ran into the chambers to warn his colleagues, but other assembly members pulled him behind some benches.
As local lawmakers hit the floor, screaming in panic, journalists who had been covering the parliamentary session hid behind their press desks.
"The man strode through the whole floor, shooting at people," Swiss Telegraphic Agency reporter Dominik Hertach told Swiss television.
Mr Hertach said that there was then an explosion, that blasted off doors and shattered windows, and smoke filled the room.
"There was blood everywhere", he said, with casualties lying on the floor and small fires burning in the assembly hall.
Chaos
Viktor Schaech, who runs a shop opposite the parliament building, said he was chatting to a friend when he heard the sound of shooting.
Zug Mayor Christoph Luchsinger said the assembly after the attack was "a terrible scene of horror, you cannot imagine it".
The attack has shattered the population of the normally tranquil Swiss town.
"It is just tragic that something like that can happen in our little canton. It is just horrible," one passer-by said.
Although police say the shooting spree is not connected to the attacks in America, the scenes of devastation seen on 11 September have taken their toll everywhere.
"After the events of September 11, nothing surprises me anymore," said one woman near the parliamentary building in Zug.