Firefighters based at the fire station nearby had heard shouting in the street and went out to investigate, where they were confronted and threatened by the man.
The 26-year-old suspect remained hostile and struck the window of one of the first police cars when they arrived.
Eyewitness Jenilee Graham said she was unaware there was a situation developing until a woman stopped her and told her to get away.
The 23-year-old City worker, from south London, said:
"I was coming back from Asda with my mum when we saw a woman who told us to stop where we were going. We didn't know what was happening, but then we saw the man who the woman was talking about pop out from behind a bus. He ran towards us, then he darted down a side street. It was obviously pretty scary."
More top news
Arsenal managed to beat Everton at the weekend but it wasn't enough to finish in the top for the first time in Wenger's time at the club.
The entertainer was held for the murder of Stuart Lubbock, who was found dead in his swimming pool in 2001, but never charged.
Although the diamond was believed to be cut in the 19th Century, its history and how it arrived at the car boot sale is unknown.