The 71 people found dead in an abandoned truck in Austria are believed to be Syrian migrants.
Three people including a man thought to be the truck owner were in custody in neighbouring Hungary on Friday in connection with the tragedy.
Three young boys age 8-11 were among the victims, as well as a baby.
Police said a Syrian travel document indicated that at least some of the victims were from that country.
On Thursday police in Hungary arrested seven people.
The truck owner, a Bulgarian of Lebanese origin, and two drivers remained in custody on Fridat, while the other four were released later.
A police spokesperson said the arrested men were members of a joint Bulgarian-Hungarian people smugglers' gang.
Local Austrian NGOs have expressed shock and dismay over the event.
“This tragedy was not necessary,” says Kristof Reibel of Diakonie, an organisation that works with asylum seekers in Austria.
“These 71 people are dead now and we have to recognise that was a direct result of the current European asylum policy. People put themselves in the hands of the smugglers and this is what happens.”
To prevent similar cases in the future, Reibel says that the focus of the fight against human trafficking is wrong.
“Everybody speaks now about enforcing the fight against the smugglers," he told RFI. "But if you put more pressure on the smugglers, then the hiding in the cars and in the lorries will become more dangerous then it is now. Because the smugglers do not want to get caught by the police.”
Others suggest different solutions.
“They should consider a humanitarian visa for Syrian refugees,” says Klaus Hofstaedter of Asylkoordination Oesterreich. “During the Yugoslavian war, there has been a comparable situation and politicians found an adequate solution to the situation by handing out humanitarian visas."
In October Austria has a general election and immigration is high on the agenda. The far-right Bündnis Zukunft Österreich party is exploiting public unease about the growing influx of immigrants to gain more political influence.
The government seems unwilling to tackle the question of giving shelter to asylum seekers, the NGOs argue.
“We have a big problem with the people that apply for asylum,” says Reibel. “But on the other hand there are a lot of empty beds in Austria. Austria is a tourist country that houses millions of people every year, yet it is not possible to provide a few thousand refugees with proper accommodation.
"If there was the political will, the housing problem for refugees could be solved tomorrow,” he says.