Shawn Tyson guilty of murdering two Britons in Florida
The pair, who met at Sheffield University, were killed after drunkenly wandering into the Newtown area in the early hours of 16 April 2011.
The court heard Shawn Tyson, 17, killed them after trying to rob them.
It also emerged that hours before the murders, Tyson had been released after his arrest following another shooting incident.
Tyson, who was tried as an adult despite being 16 at the time of the shooting, was given two life sentences without the eligibility of parole at Sarasota County Court,
'Shattered soul' Before sentence was passed, two of the pair's friends read out impact statements to the court.
Joe Hallet told Tyson they were "two people who if you had given them a chance would have given you the time of day".
Paul Davies described them as "good men, the most amazing men you ever met."
The families of Mr Cooper and Mr Kouzaris were not in court but said in a statement they were satisfied with the verdict.
They added: "It is a fact that we were given a life sentence when our sons were so brutally and needlessly taken from us.
"Ours is a life sentence, with no chance of parole from a broken heart, and a shattered soul."
The families also criticised the Sarasota court system that freed Tyson after a judge warned the teenager was a danger to the public following the earlier shooting, in which no one was hurt.
In the statement, the families said: "The evil of the killer is one thing, but the fact is, he would not have been on the streets had instructions to keep him incarcerated been passed from one judge to another."
When the mistake came to light the Mayor of Sarasota, Kelly Kirschener, vowed the city's prosecutors would never let anything similar happen again.
The court also saw a video made by Mr Kouzaris' parents. His father Peter, with his wife by his side, said: "The 16th of April, 2011, will be etched in the hearts and the memories of all those people who loved and had the privilege of loving James.
"Who could have imagined the tragic events that unfolded so cruelly?"
During the trial, jurors heard how Mr Kouzaris and Mr Cooper had been out drinking in downtown Sarasota before getting lost and wandering into the Newtown area in the early hours.
The prosecution said they were confronted by Tyson who tried to rob them and then shot them when he realised they had very little money.
The court heard Tyson had boasted to his friend Latrece Washington, who testified against him, that one of the men had begged for his life but he shot him anyway.
The teenager was seen by neighbours running to his house and climbing in the window just after the gunshots.
He also told another friend, Marvin Gaines, he had killed the men.
Mr Gaines said Tyson gave him seven 0.22 calibre shell casings to bury in his backyard, as well as a gun.
Mr Gaines later gave the gun to friend Jermaine Bane, who sold it for 50 dollars.
After he was threatened with a charge of accessory to murder, Mr Gaines led police to where the casings were buried. The murder weapon has never been found.