Detectives in Florida are trying to establish what led two British holidaymakers from a "night on the town" in the centre of Sarasota to a run-down, crime-ridden area of the city where they were shot dead

Detectives in Florida are trying to establish what led two British holidaymakers from a "night on the town" in the centre of Sarasota to a run-down, crime-ridden area of the city where they were shot dead in the early hours of Saturday.

The bodies of university friends James Cooper, 25, and James Kouzaris, 24, were found 15 metres apart on a street in the Newtown neighbourhood of the west coast Florida city at about 3am following an emergency call from a resident.

Each of the victims – described in tributes as popular role models who lived life to the full – had been shot "more than once", said Captain Paul Sutton of the Sarasota police department. Why they were in an area notorious for gang activity was a "key part" of the inquiry, he added.

"We want to determine what would cause two people, who are here on a vacation, to travel to a residential neighbourhood at three o'clock in the morning, where there are no open businesses or bars, none of the things you would normally think might attract someone at that time of the day.

"We know they were having a night on the town. They are both recent college graduates and good friends, and were having a night out. There's some evidence they visited a couple of downtown establishments during the night before and in the early morning hours of the day they were killed."

Among the theories police are investigating is that Cooper and Kouzaris were involved in a drug deal, although they say they are looking at all possibilities including that they were victims of a robbery. No drugs, weapons or large amounts of money were found at the scene.

The two, who met as students at Sheffield University, were on a three-week holiday with Cooper's parents and were staying at an upmarket resort on the exclusive barrier island of Longboat Key, 12 miles from where they were shot.

A 16-year-old male suspect arrested 24 hours after the shootings following a tip-off was named as Shawn Tyson. The teenager was previously arrested on 7 April for aggravated assault with a handgun and lives in "close proximity" to the murder scenes.

Sutton said earlier much work needed to be done before details were released of how Cooper, from Warwick, and Kouzaris, from Northampton, were killed.

"I'm not going to talk a lot about their injuries but I will say that each of them had more than one gunshot wound," Sutton said. He ruled out a claim that a Newtown resident heard machine-gun fire, and corrected earlier erroneous reports that at least 20 bullet casings were recovered. "The crime scene investigators found no shell casings," he said.

At a detention hearing in Sarasota on Monday that Tyson did not attend, a judge gave prosecutors 21 days to decide if he will face trial for murder as a juvenile or adult. Florida retains the death penalty for offences including felony murder – when a killing is committed in the course of another crime – and first-degree murder.

City leaders in Sarasota portrayed the killings as a rare occurrence as they promised the community's support to detectives. Marlon Brown, the deputy city manager, said: "Any loss of life is always something we take seriously. I offer condolences to the families of the deceased and we'll do everything in our power to piece things together and get it solved quickly."

James Roe, head coach at Kenilworth Tennis, Squash and Croquet Club in Warwickshire, where Cooper was a member, said it was tragic. "None of us are sure of the ins and outs of what went on and how he came to be in that situation," he said. "For somebody to die in that manner, to be murdered, to be shot, it is just bizarre."

"He was a normal guy, he had a very responsible job as a coach. He was an only child and was the apple of his mum and dad's eye," adding that Cooper had once played against Andy Murray.

Mark Tennant, a director of inspire2coach at the University of Warwick, where Cooper recently became head tennis coach, said: "We will remember James with great fondness, as a great guy, as a talented coach, a committed team member and, above all, a close friend."

Kouzaris had spent several months travelling in South America before his death, visiting Ecuador, Argentina, Brazil, Colombia and Bolivia. He captained a team at the Old Northamptonians Rugby Club from the age of nine until he went to university, former coach Peter Bason said. "He developed into a very fine rugby player and also a good leader, he was captain here and also at his school." He said he had been popular and likeable.