The Austrian authorities hope three people arrested in Hungary will lead them to those behind the deaths of 71 refugees and migrants found inside an abandoned truck.
Police sent to investigate the vehicle, which had been dumped on a motorway near Austria's border with Hungary, discovered the decomposing bodies on Thursday morning, local time.
The 59 men, eight women and four children are thought to have been dead for one-and-a-half to two days.
Police said they were thought to include a group of Syrian refugees. It is unclear how they died.
They originally estimated that between 20 to 50 people died in the vehicle.
The victims were probably already dead when the vehicle crossed into Austria from Hungary, authorities said.
The vehicle was towed to a customs building with refrigeration facilities in Nickelsdorf on Thursday.
Forensic teams worked through the night to examine the bodies.
The vehicle bears the logo of a Slovakian poultry company, Hyza, which said it no longer owned the vehicle - but the buyers had not removed the branding.
Hans Peter Doskozil, the police chief in the Burgenland province where the lorry was found, said it was a refrigerated vehicle - not the typical choice for people smugglers, he added.
The lorry, which has Hungarian number plates, is understood to have left Budapest on Wednesday morning.
'Warning to Europe'
Tens of thousands of refugees and migrants from conflict-hit states in the Middle East and Africa have been trying to make their way to Europe in recent months.
Some of them pay large sums of money to people smugglers to get them through borders illegally.
German Chancellor Angela Merkel, in Austria for a summit with Balkan leaders on the migrant crisis, said she was "shaken" by the "horrible" news.
"This is a warning to us to tackle this migrants issue quickly and in a European spirit, which means in a spirit of solidarity, and to find solutions," Mrs Merkel said.
- BBC / Reuters