A leading drugs expert has warned the dealer selling the white heroin thought to have caused deaths in Amsterdam could be acting « vindictively ».
On Tuesday two British men aged 20 and 21 died in a hotel room in the city, apparently after snorting white heroin they thought was cocaine.
Police in the Netherlands think the dealer doesn’t know what he is selling.
But Dr Adam Winstock tells Newsbeat it is more likely he is « wilfully knocking out white heroin as cocaine. »
The latest deaths follow that of another British tourist in the city in similar circumstances last month, and 14 other cases since mid-September where tourists have had to be hospitalised.
Dr Winstock, founder of the Global Drugs Survey, says the situation is « terrifying », not least because the dealer might be selling the product on purpose.
He describes the drugs market in the Netherlands as « sophisticated » and says there are probably different markets for heroin and cocaine.
« It’s unlikely an incompetent dealer got their batches mixed up, » he says.
« White heroin is three times more expensive than cocaine in Amsterdam, and drug dealers are businessmen driven by profit. »
Dr Winstock thinks dealers will have checked what they are selling after a widespread campaign to raise public awareness of the situation in the past month.
« Cocaine and white heroin are cut with different things, and might feel different when you snort them, » he says.
And although not all drug dealers will try their own product, Dr Winstock tells Newsbeat: « Testing for drug purity in Amsterdam is really quite easy. You can go along and get your drugs tested at government sponsored organisations where they will give you a breakdown of what’s in the drug. »
« Given the fact that most dealers are unlikely to be stupid enough not to have checked what they are selling, we are left with the uncomfortable possibility that someone is wilfully knocking out white heroin as cocaine and it’s leading people to die.
« Until proved otherwise I think that there is someone out there who knows what he is doing – one rogue dealer that for whatever reason thought ‘I’m going to teach you guys a lesson’. »
Newsbeat spoke to Rob van der Veen, from the Netherlands police, about whether the dealer could be selling the white heroin deliberately.
« We hope he isn’t. We don’t know until we find him, and there are many possible scenarios, » he says.
Mr van der Veen says the police think the dealer doesn’t know what he is selling, and may have stolen the drugs: « If you have ripped [stolen] it, it doesn’t matter about the price, there’s no loss just profit. »
« We have a lot of people undercover on the streets looking out for him, » he adds.
The police think it’s one dealer acting alone, because otherwise there would be more cases.
They’ve offered a reward of 15,000 euros (£11,939) for information, and say the dealer speaks « good English », is between 35 and 40-years-old, has « dark skin », and rides a bike.
Whoever the dealer is and whatever their intentions, Dr Winstock says people must « be unbelievably careful » if they buy drugs.
« Make sure you’re with someone to keep an eye on you, take the tiniest amount possible, don’t re-dose quickly, and don’t have alcohol or other drugs on board – and if you don’t feel well get yourself to the hospital as soon as possible. »