Philippine authorities arrested a man Saturday who allegedly sold illegal drugs at a Manila rave earlier this month where five people died from suspected overdoses, an official said.
Autopsies of three of the May 21 victims confirmed they died from heart attacks, but toxicologists have begun testing the corpses for a cocktail of illegal substances, including MDMA.
"Taking these pills together with alcohol... may lead to a heart attack," Joel Tuvera, chief of the National Bureau of Investigation's anti-narcotics division, told a news conference.
The five victims collapsed and died as some 14,000 people attended the the open-air concert headlined by Belgian DJ duo Dimitri Vegas and Like Mike.
Among the fatalities was a 33-year-old foreign man, believed to be from the US, police said.
Officers arrested the suspect Joshua Habalo in a sting operation early Saturday after an informant identified him as one of up to 10 people who sold illegal drugs at the rave, Tuvera added.
The suspect was nabbed at an event at a Manila hotel that he had organised, Tuvera said.
At the party Habalo allegedly sold an undercover agent five ecstasy pills and was carrying other suspected narcotics, including cocaine, Tuvera said.
Police are continuing to search for the nine other unidentified suspects, he added.
The party deaths come as president-elect Rodrigo Duterte pledges to target drug-related crimes in the Philippines by any means necessary when he takes office on June 30.
Duterte has vowed to use police sharpshooters to kill drug dealers who resist arrest and urged congress to pass a law to restore the death penalty.
On Thursday Duterte described the concert deaths as "unacceptable", blaming them on drugs.
"It was a deadly mix intended to kill people," he said. "When you mix downers with uppers and put it in the brain of a human being that is what happens."