On 24 May at Bristol Crown Court, Christopher Sean Simmonds, 28, below, from London, has been found guilty of killing Roger Millar, right.
This is in addition to Shelton Sibanda, bottom, 19, of no fixed abode, Swindon, who pleaded guilty to murder at an earlier hearing.
Zacharious Kori Clayton, 19, Kendel Lamtus Joseph, also 19, and 18-year-old Eurico Camotin Simoes Tavares were found not guilty of manslaughter.
Mr Millar, of East Street, Swindon was stabbed to death in the Rodbourne area of Swindon on 6 June 2012.
Detective Inspector Matt Davey of the Major Crime Investigation Team at Wiltshire Police said: "This case offers a stark reminder of the dangers of getting involved in the world of illegal drugs.
"The investigation quickly established that this incident started with an altercation between two groups over the illegal supply of drugs and, although 19-year-old Shelton Sibanda pleaded guilty to murder, the jury were asked to decide to what extent a number of others participated in Mr Millar’s murder.
"Today 28-year-old Christopher Sean Simmonds has also been convicted of his murder. Simmonds also pleaded guilty to attempting to pervert the course of justice.
“I would like to thank my investigation team who remained committed throughout the last year to bringing this complicated case to court. I am also grateful to the swift and professional response to this incident by uniformed colleagues who tried in vain to save Mr Millar’s life and secured the early arrest of two suspects in this case.
"Lastly, I would particularly like to thank the numerous members of the local community who provided valuable information to my investigation team throughout the course of the enquiry.
“Our thoughts however at this time remain with Mr Millar’s family. They have acted with dignity throughout this investigation and I hope that this verdict goes some way to providing closure to them."
The investigation was a collaborative effort under Operation Brunel.
Operation Brunel represents the collaboration of Major Crime and Special Branch units from Wiltshire Police and Avon & Somerset Police.
The collaboration formally went live in January 2011, and strives to ensure greater resilience and improved responsiveness become the hallmarks of the new Major Crime Investigation Team (MCIT) and Special Branch (SB) service operating across the Avon and Somerset and Wiltshire force areas.
Family statement following the Roger Millar murder trial
"The Millar family takes no gratification from the verdict that has come today as no verdict would ever be able to bring Roger back.
"However we do take satisfaction in the fact that the Justice system in our country works and works well as shown by the result today.
"The passing of our brother Roger has left a large whole in the lives of everyone he came in contact with.
"Roger was the complete gentleman and has been described so, not only by the Millar family but colleagues that he worked with whilst serving his country With the Corps of the Royal Engineers both home and abroad.
"We would like to thank Mr Lickley QC and the Crown Prosecution Service along with Detective Inspector Matthew Davey and the Major Crime Investigation Team from Wiltshire Police for all the hard work and dedication that they have shown throughout the whole of this case.
"We would also like to thank Audrey Carson and the staff from the Victim Homicide Service for their great work and support that they have shown to our family and close friends during this difficult period."