US detectives are investigating how two British holidaymakers came to be shot dead in a rundown neighbourhood in Florida.
University friends James Cooper, 25, and James Kouzaris, 24, were murdered in a deprived part of the city of Sarasota in the early hours of Saturday.
Local officers said it was "very unusual" to find tourists in this area, which is about 12 miles away from the upmarket island city of Longboat Key where the pair were staying.
Sarasota police said the Britons were not carrying any drugs but would not confirm whether they had any money or weapons.
A 16-year-old boy has been arrested and charged with two counts of murder.
Mr Kouzaris, from Northampton, was on a three-week holiday in Florida staying with Mr Cooper, from Warwick, and his family.
The former Sheffield University students were found shot dead 50ft from each other in a street in the Newtown area of northern Sarasota at about 3am on Saturday.
Captain Paul Sutton, of Sarasota police, said there was no known link between the suspect and the victims.
"We are still investigating why they would have been in this area," he said.
"It is very unusual to find tourists or visitors in this area. It is a residential neighbourhood with no shops and no bars. We do not know what brought them here at 3am."
Friends and family said Mr Kouzaris, who was known as Jam, "lived every day to the fullest" in heartfelt tributes on his Facebook page.
His cousin Lynn Hucker wrote: "To a beautiful cousin who I will never forget. Always happy and full of life. You will be so sadly missed James."
A friend called Ben Stacey added: "RIP Jam, absolute legend. It was an honour mate, I was so looking forward to seeing you again in Miami. The month travelling with you was some of the best times I've had and was so thankful I met you. Rated you very highly XO."
Mr Kouzaris spent several months travelling in South America before his death, visiting Ecuador, Argentina, Brazil, Colombia, Bolivia.
In a message on his Facebook page he spoke of looking forward to returning to Britain on March 27, writing: "Back to normality soon."
Mr Cooper, who worked as a tennis coach for University of Warwick-based company inspire2coach, replied: "U have got to be kiddin, ur back a week and then we go off to america."
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, according to a 2009 US Department of Justice study.
A Foreign Office spokesman said: "We can confirm the deaths of two British nationals on holiday in Sarasota on April 16.
"Next of kin have been informed and consular staff are providing assistance.
"Sarasota police have launched an investigation and have made an arrest. We cannot comment further on the investigation."
Mr Kouzaris' and Mr Cooper's personal tutors from the University of Sheffield also paid tribute to the men.
Ed Ferrari, Research Fellow from the university's Department of Town and Regional Planning, said: "It is with immense sadness that I learned today that one of our former students, James Kouzaris, was tragically killed in Florida.
"I was James' personal tutor in 2008 at a time when he was completing his four year degree course in Town Planning.
"James was committed to his studies and was a skilled Planner but, more than that, he was a friend to many in our department.
"His positive outlook and humour were infectious and he involved himself totally in the life of our department and University.
"He was just the sort of student any lecturer would hope to have in their class."
Dr Jon Burchell, Senior Lecturer from the university's Management School, said Mr Cooper was a student in the school and was one of his personal tutees.
"During his time in Sheffield, James was an enthusiastic and hard working student, and was popular among his peers," he said.
"He had a good sense of humour and a range of plans for what he wanted to do after graduation.
"I am immensely shocked and saddened by the news and send our deepest condolences to his family."
Before studying at university, Mr Kouzaris attended Northampton School for Boys.
Headteacher Michael Griffiths said the 24-year-old was at the school from 1999 until 2004, joining the school in Year 9 and staying to study for his A-levels.
Mr Griffiths said he was captain of the school's rugby team and led them on a tour of New Zealand and Australia in 2002.
"His rugby coach said he was a smashing lad, always had a smile on his face, was gregarious, good company and somebody who was always keen for new challenges," he said.
"He was extremely popular, he was keen to do well in his studies, he was very popular with other students and with staff, a really pleasant, amiable young man.
"This is obviously a tragedy and our thoughts are with his family today."
Sarasota police said Mr Kouzaris and Mr Cooper were shot in a narrow one-way street in a neighbourhood of social housing.
Questions have been raised about how the British tourists got to the area as they did not have a car and the city's public transport does not run at 3am, officers said.
Capt Sutton refused to be drawn on why Mr Kouzaris and Mr Cooper were there at that time, saying detectives were "trying not to have tunnel vision" as they sought to establish what happened.
Asked whether there could be more arrests in the case, he said: "We're looking at the possibility. More than one person ran when the shots were fired.
"Is that other people involved or is it people who just happened to be there?"
Post-mortem examinations have been carried out, meaning the bodies of Mr Kouzaris and Mr Cooper can be released to their families to be brought back to Britain, the spokesman added.
Mr Cooper's employers paid tribute to him in a written statement, describing him as a "great guy" and a talented tennis player who once represented his county.
Mark Tennant and Richard Marklow, directors of inspire2coach, said: "We are truly saddened by the sudden death of our friend and colleague James Cooper.
"James and his friend were shot dead whilst on holiday in Florida.
"James was a young tennis coach and a key full-time member of the inspire2coach team.
"He had recently been promoted to a head coach role within the company, which he was due to start on his return from holiday.
James was a graduate from University of Sheffield and a Warwickshire County tennis player. He was undertaking an LTA senior coach course, and was due to complete his final assessment in a few weeks' time.
"We will remember James with great fondness, as a great guy, as a talented tennis coach, a committed team member and, above all, a close friend.
"We shall all miss him very much and our thoughts are with his family at this difficult time."
Mr Kouzaris captained a team at the Old Northamptonians Rugby Club from the age of around nine until he went to university, a former coach said today.
Peter Bason, who coached and played for the club, said: "He started just before he was nine or 10 and carried on through his teenage years until he went to university.
"He developed into a very fine rugby player and also a good leader, he was captain here and also at his school.
"He was a very likeable lad, very popular amongst all the other lads and coaches.
"I've had so many phone calls and emails today from people who are so shocked, it's very, very sad.
"Once he went to university we lost contact a bit, but we heard bits about what he was up to from other people and we knew he had done extensive travelling."
Mr Bason said he did not know anything about Mr Cooper, but said Mr Kouzaris was liked by everyone he met, adding: "There wasn't anyone who had a bad word to say about him, he was just a very likeable young man."
A friend and former tennis coach of Mr Cooper described the circumstances surrounding his death as "bizarre".
James Roe is head coach at Kenilworth Tennis, Squash and Croquet Club, where Mr Cooper had been a member since he was a toddler.
He said: "I found out what had happened from his best friend on Saturday, it is very tragic.
"None of us are sure of the ins and outs of what went on and how he came to be in that situation.
"We know how he died but why he died is what we want to know.
"For somebody to die in that manner, to be murdered, to be shot, it is just bizarre."
He added: "He was on a family holiday, his mum and dad were out there and he knows Florida very well.
"He decided to take a two-week holiday because there was not much coaching on over Easter.
"I believe his parents are still over in Florida."
Mr Roe said he coached Mr Cooper when he was a 14-year-old county player, representing Warwickshire.
He said: "He started off as a pupil but he became a really good friend.
"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.
"He did really well at school and then at university. He was a model student and a cracking tennis player.
"It is a sad loss because he had a flourishing tennis career ahead of him. He was really going places.
"He is going to be sorely missed in the tennis world."