A man was stabbed twice in a "calculated and violent" attack by a stranger he had agreed to meet in order to sell him his laptop, police said.
The victim, in his 40s, was knifed after arranging to meet a man to finalise the sale of a Macbook Pro.
They met at the victim's place of work in Finchley High Road, where the suspect's demand for a receipt before money had exchanged hands left the vendor "uneasy" about the sale.
He tried to walk away, but was grabbed by the suspect who told him he had a knife before grabbing the laptop and stabbing the victim int he back and the shoulder.
The suspect then fled the scene and the victim was treated in hospital for his injuries.
Detectives have now released CCTV of a man they wish to speak to in connection with the attack on January 14.
DC Hussain Ahmed of Barnet Police said: "This appears to be a calculated and violent attack with an element of preplanning.
"The suspect attending the meeting armed with a knife and showed no hesitation of using it to steal the laptop. He has left his victim devastated.
"Whoever carried out this attack is a dangerous man and I would appeal to anyone who recognises him to call police immediately."
Anyone with information should contact Barnet Police or call Crimestoppers anonymously on 0800 555 111.