The family of an Aylesbury man shot in the head and arms say they are disappointed no one has been brought to justice one year on.
Kevin Williams, 34, was left in a critical condition and suffered life-changing injuries in the Stour Close shooting on March 28 last year.
A £2,000 reward is now being offered by Crimestoppers for information leading to the arrest and conviction of anyone involved.
Four people have been arrested in relation to the shooting, but all were released without charge and police have no new suspects.
In a statement Mr Williams’ family said: “This incident was a tragedy for our family and something which has absolutely changed our lives.
“Until Kevin receives justice, we feel unable to move on as a family and so we urge anyone with information to get in touch with police.
“It is so disappointing that the criminals behind this callous attack have not yet been brought to justice.”
Police investigations are continuing and it is hoped the reward will tempt someone to come forward.
Limited evidence at the scene and a lack of witnesses has hampered investigations, with police unable to identify the only person seen at the scene around the time of the morning shooting.
Police say Mr Williams was targeted but don’t know why. It is thought he will need medical care for the rest of his life.
Senior investigating officer Det Ch Insp Gill Wootton said: “We have been unlucky, although I believe in making your own luck.
“We have not had the volume of the normal evidence you might get at a crime scene, such as CCTV footage.
“I’m confident that someone out there will have information that will assist us.”
Anyone with information can call anonymously on 0800555111 or police on 101.