One of the youths thought to have been the target of the gang who accidentally shot five-year-old Thursha Kamaleswaran has contacted police.
The news came as sources revealed that up to 50 gangs operate in the area where Thursha and another bystander became innocent victims of a vicious turf war.
Detectives investigating the shooting at the Stockwell Food and Wine Shop in south London on Tuesday night have called in Territorial Support Group officers to reassure locals fearing "tit for tat" attacks.
Chief Superintendent Nick Ephgrave called for people in the area to come forward if they have information about the "truly shocking event".
A shopkeeper, believed to be Roshan Selvakumar, 35, was also hit, suffering a head wound during the attack.
They were caught up in the violence when two black youths cowered in the store after being chased by three other black youths on bicycles.
As the pair hid inside, one youth stopped at the door and opened fire indiscriminately.
The three attackers, who a witness said were aged between 14 and 17, fled from the Stockwell Road shop along Broomgrove Road and into the Stockwell Park Estate.
The victims, who police said were Sri Lankan and unrelated, were rushed to hospital in south London.
They are both in a critical but stable condition.
Thursha was visiting relatives when the attackers struck.
Crimestoppers are offering a £50,000 reward for information leading to the gun attackers' capture, it was also announced.
Police said the girl's brother and sister were also in the shop at the time of the shooting, but they were unhurt when two shots were fired.
Officers are still painstakingly searching through CCTV in a bid to track down the culprits, Detective Chief Inspector Tony Boughton told reporters at the scene in Stockwell.
"We are beginning to get a clearer picture of what happened," he said.
"One of the youths who first ran into the shop has come forward to police and is assisting us with our inquiries.
"We are still trying to trace the other individual and appeal to him to come forward."
Thursha had been visiting the shop's owners, her aunt and uncle, when the attack took place.
"With Thursha and her mother were her siblings. A three-year-old girl and a 12-year-old boy."
The teenage target who came forward to police has told officers that he ran in to the shop to take cover.
Initial forensic reports support witness statements that two shots were fired.
Evidence is being analysed at forensic labs to see if it can be linked with other crimes, detectives added.
"There's a lot of CCTV in the area and we are trying to follow a continuity trail to find the youths responsible," Mr Boughton said.
He said they had already had a good response from the local community in their appeal for information.
"We continue to appeal to anyone who might have seen these three youths who were responsible cycle around Stockwell between 8pm and 10pm on Tuesday night," he added.
Both the child, believed to be London's youngest gun crime victim, and Mr Selvakumar remained in a critical but stable condition with family members at their bedside.
Mr Ephgrave, the borough commander, said he had requested extra support from Scotland Yard to reassure the local community.
"You should see in the next few days some reassurance that this is an isolated incident," he said.Reuse content