The teenager was dragged into bushes on Railway Street on Monday evening.
Grays: Two Bailed Over Bucks Shooting
Two people arrested in Essex after a man was found with gunshot wounds to his arm and head have been bailed by police.
The 33-year-old man and 32-year-old woman were detained in Grays on suspicion of conspiracy to commit murder in connection with a shooting in Buckinghamshire.
They have been bailed until September 19, Thames Valley Police said.
The 33-year-old victim is in a serious condition following the incident in Stour Close, Aylesbury at about 10am on March 28.
Detective Chief Inspector Gill Wootton, the senior investigating officer, said: "We do not believe this was a random attack and believe the victim was specifically targeted at his home. Although he was a resident in Aylesbury, he spent a lot of his time in the north-west London area where he grew up.
"I am still appealing to members of both communities to come forward if they have any information which could assist our investigation. A number of people have already come forward and have spoken with officers but we believe there are still people out there with information they have not yet shared with us. Now is the time to do so.''
Police want to speak to a man dressed as a delivery driver, who was seen in the Stour Close area between 9.30am and 10am on March 28.
He is white, in his 40s, about 5ft 9in and was wearing a dull-green uniform and carried a clipboard, a police spokesman said.
Officers also want information about any suspicious people or vehicles seen in Stour Close both on the day of the shooting and on the days leading up to it.
Two other men, aged 35 and 38, who were arrested in London in June on suspicion of conspiracy to murder and attempted murder are on police bail until August 28.
Anyone with information should call DCI Wootton on 101 or Crimestoppers anonymously on 0800 555 111.
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