Mark Duggan pulled a gun from his waistband before armed police shot him dead in north London, a court heard.
A firearms officer told Snaresbrook Crown Court he saw Mr Duggan holding a weapon before he was shot.
Kevin Hutchinson-Foster, 30, denies giving Mr Duggan an illegal handgun 15 minutes before he was intercepted in Tottenham on 4 August last year.
Mr Duggan's shooting sparked riots in Tottenham which spread across London and then to cities in England.
Giving evidence in Mr Hutchinson-Foster's trial, the firearms officer told the court however, that when he went over to Mr Duggan he could not find a gun.
Identified only as W70, the officer gave evidence from behind a screen in the court.
Prosecutors allege Mr Duggan was travelling in a cab from Leyton to Tottenham having picked up a loaded gun from Mr Hutchinson-Foster.
The officer recalled his firearms team had received a "state amber" at 18:00 on 4 August, which meant there was enough intelligence to arrest a suspect.
Thirteen minutes later, as he waited in an unmarked police car two cars behind Mark Duggan's cab, the officer said they received a "state red" over the police radio and the order "doors, doors", to leave the vehicle.
"The side door of the taxi was slid open," he said, and police officers were repeatedly shouting "armed police" at Mr Duggan.
"I saw the subject pivot out of the door in a stooped position," he said.
'Where's the gun?'
"His right hand was crossed across his body with the hand inside the left hand side of his jacket towards his waistband, his left hand was holding the lower part of his left lapel.
"It very much appeared he was concealing something.
"As he pivoted... at the same time he very quickly drew out his right hand from the left hand side of his waistband and he was holding a self-loading pistol or handgun."
The officer said he heard two shots to his left as Mr Duggan drew his right hand out of his jacket.
He said he caught hold of Mr Duggan's wrists as he fell to his knees and shouted: "Where's the gun?" but failed to find one and started first aid.
When Stuart Denney, QC for the defence, asked him: "Where was the gun?", W70 replied: "I have no idea".
The officer also told the court he omitted the fact Mr Duggan was armed from his initial statement after meeting lawyers and Police Federation representatives.
When asked if this was a deliberate act, he said: "I don't know."
He also denied "seeing any sign of a police officer bringing a non-police gun to the scene".
The case continues.