Austrian police said on Friday that the 71 bodies found in an abandoned truck on an Austrian motorway were believed to be those of Syrian refugees and included a toddler and three young boys.
The arrest came after the Austrian interior minister on Thursday vowed to find the criminals who were responsible for the brutal incident, adding that there would be zero tolerance shown towards any that were caught.
Hungarian police have arrested three Bulgarians and one Afghan citizen related to the truck found in Austria in which 71 refugees have died, police departmant said in a statement on Friday on its official website.
"Among these 71 people, there were 59 men, eight women and four children including a young girl one or two years old and three boys aged eight, nine or 10," police spokesman Hans Peter Doskozil said.
"In addition, police have conducted house searches ...and questioned almost 20 people as witnesses," police said in the statement.
"There was also a Syrian travel document found so of course our first assumption is that these people were refugees, and likely a group of Syrian refugees. We can rule out that they were Africans."
Doskozil also said that three people were in custody in Hungary over the tragedy, one believed to be the owner of the truck found on a motorway lay-by and two others who were driving.
One is a Bulgarian citizen of Lebanese origin believed to be the owner of the vehicle.
The others, a Bulgarian and another with Hungarian documents, are "pretty certain to be those who drove the vehicle," Doskozil said.
The truck was discovered on Thursday near a highway close to Parndorf town in Burgenland state, some 50 km southeast of Austria's capital Vienna, according to the Krone newspaper.