The teenager was shot dead in a taxi in Tividale in the early hours of June 20 last year after chased down by a group in another car.
During the trial, the court heard how 24-year-old Campbell released music on Spotify, Apple Music and Soundcloud under the name Kash, in which he boasted about drug-dealing empire and violence meted out to rivals.
He filmed videos in Tipton riding around in a Rolls Royce bragging about how much crack and heroin he sold, how he would cut the drugs to make more money and his readiness to use a gun if needed.
Campbell was invited to record a song and video for urban media platform P110, which helped Jaykae, Skepta, Mist, Giggs and Bugzy Malone on the path to mainstream stardom.
In the video for P110’s Hood’s Hottest 2, the 24-year-old can be seen getting out of a Rolls Royce wearing his distinctive “Kash” gold and diamond necklace.
Filmed at Dudley Port hand car wash and valet, the video featured a luxury BMW, Mercedes and expensive quad bikes. Surrounded by masked men drinking brandy Kash immediately boasts about his burgeoning drug empire.
His opening line being: “I put the food on the scales and tell my young boy to wrap it up” and also raps about “mountains of snow (cocaine) and “reloading half a b (kilo)”.
WARNING: Video contains language viewers may find offensive
Mimicking shooting a gun Campbell warns he happily will enter drug rivals’ “trap houses” and ” still kidnaps and do acid attacks”.
The trial at Birmingham Crown Court heard how Aston teenager Kimani Martin befriended Campbell at a music studio. Then, after arranging to meet Campbell for a drug deal, he kidnapped him and Luke Adams at gunpoint, forcing them to hand over money and a mobile phone with a “drugs hotline” as its number.
Mr Martin and his two associates also stole Campbell’s “Kash” necklace. Robbing a rapper’s personalised jewellery and parading it on social media is a staple of American hip hop feuds, and Campbell would have known his humiliation would have complete within a few hours.
An associate of Kimani Martin, who did not want to be named, told the Express & Star: “Kimani loved having a laugh and he would have been showing off the necklace on Snapchat as soon as he could.
“He was only 18. No-one deserved to be murdered. What happened to him has made a lot of us grow up and look at our lives.”
The necklace was found in the back of the taxi in which Kimani was shot dead, and provided detectives with their first major lead in the investigation.
Detective Inspector Jim Colclough, from West Midlands Police Homicide Squad, said detectives also found Campbell’s mobile phone, so used it to ring his mother and find the rapper.
He said: “We never did track down the two people with Kimani in that taxi. However, they are lucky to be alive because we believe those in the car acted together.
“We know after the first shot, the Golf circled around and the driver asked the taxi driver where the other two were. We could easily have been dealing with a triple murder.”
Campbell, of Vicarage Road, Tipton was charged with murder, along with 22-year-old Usman Amjad of Wood Green Road, Wednesbury and Atif Khan, 25, from Park Lane in Tipton.
He added: “We charged all four with murder under join enterprise because they would have knew Campbell wanted revenge. Whilst in the Golf several calls were made to 1-2-1 Cars to try and locate the taxi which had picked Martin up. We don’t believe they were given any information but they tragically spotted the taxi leaving Tipton and gave chase.
“They knew he had a gun, this was not a revolver hidden in his pocket which he pulled out seconds before the shooting. He had a shotgun which have long barrels, they would have all seen him and were encouraging him to use it”
In a chilling boast which foreshadowed future events, Kash raps “He always keeps a strap (gun) close to him”.
During the trial the jury heard that within an hour of being freed by his captors, Campbell had a loaded shotgun in his hands and was ready to kill while Khan drove a stolen Volkswagen Golf to hunt Kimani down until he was found and shot in Dudley Road East.
Campbell being taken off the streets gave particular satisfaction to detectives in the West Midlands Police, whom the rapper regularly goaded in his music and videos.
Smiling at the camera he taunts: “Drugs squad from my teens still trying to raid me.
“Drugs squad trying to find out where ****** at, I’m up at Harvey Nicks about to spend two wraps (£2,000).”
DI Colclough said: “Clearly you can see Campbell was a danger to society. He no regard for the law and a total disregard for human life. If crossed he was willing to exact fatal revenge.”
The homicide squad, which is now comprised of detectives and civilians, built a watertight case against Campbell.
The 24-year-old lied for 11 months about his role in the shooting by continually claiming there was a fifth person in the car who shot Kimani.
However, in a remarkable turn of events during cross-examination by Khan’s lawyer Campbell admitted being the shooter after fellow defendants refused to back up his lies.
The cocky bravado of his persona as a rapping drug kingpin living the fast life crumbled in the dock as he began crying when confronted with the tragic consequences of his actions.
Campbell’s admission even surprised his legal team, his defence barrister Stan Reiz QC told the jury he had been misled, and then entered a plea of manslaughter which prosecutors rejected immediately.
The jury made short work of Campbell’s guilt as a murderer but then had to decide whether the other occupants of the VW Golf were an execution squad or confused young men in the wrong place at the wrong time.
Campbell and Khan were both convicted or murder while Amjad was found guilty of manslaughter. A fourth defendant, Luke Adams, 19, from Walsall, was cleared by the jury.
Campbell, Khan and Amjad will be sentenced on Wednesday, June 29.