Prosecutors said the truck was abandoned near the village of Lokorsko after the driver and his companion found that many of the 52 migrants in the truck were dizzy and some had already died. The migrants were in hidden compartments of the truck which were isolated with foil.
The truck driver and his companion were also charged over the deaths, prosecutors said.
Despite strong and prolonged banging on the cabin, the driver refused to stop the truck earlier, the head of the National Investigative Service and deputy chief prosecutor Borislav Sarafov told reporters.
The deaths have shocked Bulgaria, in what is one of the worst incidents of its kind on the overland route across the Balkans into Europe.
Thousands of people fleeing war and poverty in the Middle East, Africa and Asia make the journey and Bulgaria has been trying to cope with an increased inflow of migrants from neighboring Turkey in the past year.
Since the Taliban took control of Afghanistan in August 2021, that country has plunged into an economic and humanitarian crisis. According to a recent report from the United Nations Office for the Coordination of Humanitarian Affairs (UNOCHA), an estimated 28.3 million – roughly two thirds of Afghanistan’s population – are in need of urgent humanitarian assistance to survive. Last month, a Taliban official said that at least 157 people had died in the country’s bitter winter.
The 18 victims died of a combination of lack of oxygen in an enclosed space and difficulty breathing as they had been crammed into the truck “like in a tin can,” Sarafov said.
“The victims died slowly and painfully,” he added.
“This case shows an extreme callousness and demonstrates that migrants are seen only as goods that should be shipped from one place to another, irrespective of whether they are alive or dead,” he said.
The other 34 migrants, who were rushed to hospitals on Friday, remain in stable condition, officials said.
Five of those charged are in custody, while one of the suspected traffickers, who had managed to flee the country, is being sought with an European arrest warrant.
Prosecutors said the ring had trafficked migrants from the border with Turkey across Bulgaria to Serbia, from where they continued their journey mainly to Britain, Germany and France.