Father-of-three Robert Lettin died after he was shot in the chest with an air rifle during an armed robbery at his home.
The 57-year-old was fatally injured when a gang of raiders burst into his house demanding cash and drugs.
When Mr Lettin was only able to hand over £500 and an ounce of cannabis, the leader of the robbers, Francis Boateng, turned the weapon on him and shot him in the heart.
The gang then escaped into the night, leaving the victim bleeding to death in the arms of his son.
Boateng, a drug dealer known by the street name KO or Knockout, was later convicted of manslaughter at the Old Bailey and jailed indefinitely for the public protection, after one of the other robbers informed on him.
Jurors heard Mr Lettin lived in Lichfield Road in Cricklewood and earned a living doing odd jobs and occasionally dealing small amounts of cannabis.
In January 2007, he sold some ‘super-strength’ Thai weed to two crack addicts, who between them owed £250 to Boateng.
Instead of paying off their debt, the pair tipped the dealer off about the possible stash and then accompanied his gang to Mr Lettin's flat on the night of January 24 that year.
Boateng and two henchmen burst into the flat armed with a knife and demanded the drugs and money.
Mr Lettin, who had his 25 year-old son Kieran visiting at the time, could only hand over an ounce of cannabis and around £500 in cash.
Boateng flew into a rage and threatened to stab someone unless more was handed over, before spotting an air rifle propped up in the corner of the room.
Kieran Lettin later told jurors how the robber then levelled the gun at his father's chest and squeezed the trigger without checking to see whether it was loaded.
The victim was struck at point blank range in the chest by a hunting pellet which was still in the rifle chamber.
In his statement to the court, Kieran letting said: 'My dad died in front of my while the man was shouting at me and prodding me with the gun that killed him.’
Boateng’s two lackeys fled the house while their leader helped himself to a laptop computer before fleeing with words: 'That's what happens when you mess with Mikey.'
Kieran dialled 999 but paramedics could no nothing to stem his father’s bleeding and Mr Lettin was pronounced dead minutes later at 6.04pm.
After the robbery the gang returned to a bail hostel in Kilburn, northwest London, to share out the spoils.
They ordered food from Pizza hut, watched a DVD of the film Blood Diamond, and 'laughed and joked' around with the air rifle.
Detectives investigating the killing at first had little information about the identity of the robbers.
But after his arrest, one of the crack addicts who had originally tipped off Boateng agreed to name those involved in the raid in return for police protection.
Following his trial Boateng, 25 at the time, was cleared of murder but convicted of manslaughter and conspiracy to rob.
He was jailed indefinitely for the public protection and ordered to serve a minimum of four-and-a-half years before being considered for release on parole.
Three other members of the robbery gang also received prison sentences after they were convicted of conspiracy to rob.
Jailing them Judge Stephen Kramer QC told the gang they had plotted a robbery to 'satisfy a craving for cannabis'.
'You all hatched a plan with the purpose of robbing him of what you all expected to be a significant stock of cannabis,’ he said.
'Sadly for him Mr Lettin did not have the amount of cannabis that you had wanted. He was only a small-time user and supplied to his family and friends.
'At your frustration at your lack of success you Boateng picked up a powerful air rifle that Mr Lettin had, pointed it at him and shot and killed him in full view of his son.
'Robert Lettin was 57 when you cut his life short and in shooting and killing him you went far beyond what the others had agreed to do.'
The robber who identified his fellow gang members to police was given a 12 month sentence suspended for two years with a two year supervision order, after pleading guilty to conspiracy to rob.
Judge Kramer told him: 'I accept that you bear no liability at all for the tragic death of Robert Lettin. You are now in the witness protection scheme and you are cut off from your family and friends.
'You are setting out on a new track on your life, drug free. I am prepared to suspend the operation of a prison sentence that must be passed on you.
'The ball is in your court. By reason of you cooperation you can count yourself very lucky.'
In a victim impact statement, Mr Lettin’s partner Jane Roberts, who was the mother of his two young children, said: 'My sons were just eight and nine when Rob died.
‘Now their whole life stretches before them, without him.
'I just wish I could sit these men in a room with my children and let them hear the screams as they go through another nightmare.
'Rob should still be here laughing with his children.'