Two 17-year-olds shot in a crowded McDonald's had earlier been arguing with other people in the fast-food restaurant, police have said.
The restaurant was packed when the shooting took place
A gunman opened fire in the restaurant packed with families, in Brixton, south London, on Thursday evening.
One youth was shot in the chest and is still in hospital. The other, who was shot in the arm, was discharged on Thursday. Both are recovering well.
The gunman is believed to have escaped on a bicycle along Brixton Hill.
He was originally thought to have escaped on foot.
The shooting took place at about 1725 BST in the restaurant at the junction of Brixton Road and Coldharbour Lane.
Families and schoolchildren were present in the restaurant at the time.
A Scotland Yard spokeswoman said: "We now know prior to the shooting the victims were involved in a brief verbal argument with some other people in the restaurant and then three to four minutes later the shooting occurred.
"It is also now known that the suspect was in the restaurant prior to the shooting and may have escaped on a pushbike afterwards along Brixton Hill rather than on foot as previously thought."
It is also thought that the victims and the suspect may have known each other, but it is not certain.
Police have said there is no evidence to suggest the shooting was gang-related.
They are continuing to search for the gunman.
The inquiry is being handled by officers from Operation Trident, which investigates gun crime in London's black community.