A gang which robbed at least 50 tourists in Rome after offering them drugged wine at a gay bar has been rounded up after allegedly killing a middle-aged American.

Police suspect that Kelly Cullen, 56, who was found dead on 14 November in the Colle Oppio park overlooking the Colosseum, was one of the victims of the gang, which preyed for months on foreigners mingling in the street outside the nearby Coming Out bar.

"The first tests showed the American – who was found robbed and partially clothed – died of a heart attack, but we suspect blood analysis will show he had a fatal reaction to the knock-out drug the gang gave him," said police official Tiziana Lorenzo.

The gang, comprising two Romanians and an Egyptian, started offering the wine spiked with benzodiazepine to tourists this summer, just as a wave of homophobic attacks on customers of the Coming Out peaked.

As their victims began to lose consciousness, the gang would guide them into the park and strip them of their valuables. "The area known as Gay Street was fertile hunting ground because of the crowds," said Lorenzo. "Foreigners were mainly picked because they were likely to have more cash and leave town without reporting the theft."

Up to 25 Americans were robbed, as well as British, Spanish, Swiss and German drinkers.

Working on a tipoff from bar staff, undercover police spotted the gang at work on 16 November. "It was a quiet night and they left empty handed, so we arranged for a "random" identity check, far from the bar, by police who confiscated their bottle of wine, which was positively tested for the drug," said Lorenzo.

"The gang did not suspect a thing and two nights later they were back at the bar and we arrested them as they escorted a drugged Swiss man in the direction of the park."