Michael Marks said he saw Karl Bishop attack Rob Knox (right)
The man accused of stabbing teenage Harry Potter actor Rob Knox to death was "winking and smiling" as he was led away by police, a court has heard.
Karl Bishop allegedly stabbed Mr Knox, 18, to death outside a bar in Sidcup, south-east London, in May last year.
A witness told the Old Bailey that he saw Mr Bishop encouraging people to confront him before the incident.
Mr Bishop, 21, from Sidcup, denies murder and five charges of wounding, saying he was acting in self-defence.
The court heard the witness, Michael Marks, was at the Metro bar when the incident took place.
He said he saw Mr Bishop on a step outside the bar "for a little while, telling people to come on" before the attack.
Mr Marks added: "The rest happened reasonably quickly."
Mr Bishop allegedly stabbed the actor five times as he tried to protect his younger brother Jamie.
Five of Mr Knox's friends were also stabbed in the attack, the court heard.
Mr Marks said there were only 40 to 50 seconds between the time he saw Mr Bishop with a knife in his hand and the actor being led away injured.
The trial continues.