Two British men were found shot dead with their shirts off and trousers round their thighs after they drunkenly walked into a rundown neighbourhood in a Florida city, a court has heard.
James Cooper, 25, and James Kouzaris, 24, were killed after they walked into Newtown in Sarasota in April last year.
Shawn Tyson, who turned 17 on Monday, is charged with two counts of first-degree murder.
Opening the prosecution case on Thursday after three days of jury selection at Sarasota Court, Assistant State Attorney Ed Brodsky said: "The reason that you are here today and what this case is about are the tragic events that occurred just shortly less than a year ago.
"[On] 16 April 2011, at approximately three in the morning, two British men who were here on vacation would find that they would die at the hands of gunfire."
Pointing at Tyson, who wore an orange shirt and tie, he said: "The evidence will conclusively demonstrate to you that this man right here is responsible for the deaths of James Cooper and James Kouzaris.
Brodsky described how the men had been out for a meal with Cooper's parents, then went drinking and left the Gator Club in downtown Sarasota, at about 2am.
Residents heard between six and eight gunshots "ring out in the neighbourhood" Brodsky said.
When police and fire and rescue services arrived at the scene in the public housing project known as The Courts, they found the men on either side of the road, shot dead.
Both men had their trousers pulled down to their thighs, and both still had their money and wallets.
They were pronounced dead at the scene, he said.
Autopsies showed Cooper was shot four times - three of the bullets went straight through his body The fatal shot went into his chest, perforated his left lung and ended up in his heart.
Kouzaris had been shot twice in the back, Brodsky said.
Brodsky said a witness would describe hearing noise outside at about 2.45am. He saw the who British men walking shirtless and "appearing to be drunk", and also saw "two black males crouching and watching them as they walked by".
"He will then tell you that approximately one minute or so later he heard gunshots ring out and that several minutes thereafter the police would arrive."
Another witness would tell the jury he saw Tyson with a fun on the night of the murder, while a witness who lived opposite saw him jump into the window of his apartment after the shots rang out.
The court heard Tyson had boasted to one witness about shooting the Britons.
Brodsky said: "He and another male saw the two men as they walked by and they decided to rob them.
The prosecutor told the court that Tyson told another witness he had "done 'em", referring to the two Britons.
Another witness, Marvin Gaines, said Tyson told him he had put the gun under his house and, when he asked why, he told him: "Those two bodies back there, I did that."
Brodsky said police searched Tyson's bedroom on the evening of 16 April and found a 0.22 calibre bullet.
After his arrest, he was recorded as telling his half-brother: "They found the bullets, it's the only thing that's going to f*** me up."
Tyson's DNA was also found on Cooper's jeans, Brodsky said.
In her opening statement, public defender Carolyn Schlemmer told the jury: "Shawn Tyson did not murder James Cooper and James Kouzaris.
"The evidence in this case will show no murder weapon or a weapon believed to even be a murder weapon was ever recovered in this case."
She said the gun and bullet casings found were not linked directly to Tyson, but to the people who had given them to police.
Schlemmer said: "You will hear about several witnesses and you are going to hear a lot, you will hear about their deals, their benefits, what they got from this case, promises made to them.
"You will hear pressures and threats used against these witnesses by the Sarasota Police Department and the State's Attorney's Office."
Tyson faces life in prison without parole if he is convicted. Relatives of Kouzaris and Cooper were not in court today, but friends arrived this morning for the trial.