NICKELSDORF, Austria (AP) — An overpowering stench of death came from the truck on Austria's border with Hungary as workers unloaded the bodies of some of the 71 migrants who perished trapped inside the vehicle they hoped would take them to a better life.

Found Thursday on the main Austrian highway leading to Hungary, the truck containing the victims' corpses was towed to a cooled border warehouse before police and forensic experts began the grisly work of unloading the partially decomposed bodies before shipping them to a Vienna morgue for autopsies.

On Friday, workers continued the work, wearing gloves and respirators as they hefted plastic body bags into coffins neatly lined up on the warehouse ramp. One after another, five trucks backed up to be loaded.

Moments after the last truck left in the direction of Vienna, about a dozen migrants scurried across a patch of the four-lane highway connecting the Hungarian capital, Budapest to Vienna.

They said they were Kurds from Syria and Iraq. Two were women carrying small babies. All seemed exhausted.

No, they said: they hadn't heard about the deaths.

As the trucks sped toward Vienna, police in Austria and Hungary worked to trace the perpetrators, announcing the arrests of several suspects.

Austrian police said three people had been arrested while their Hungarian counterparts said four were in detention. There was no immediate explanation for the discrepancy.

This year has seen tens of thousands of people risking everything to seek a better life or refuge in wealthy European countries. At least 2,500 have died, mostly at sea.

Many now travel from Greece through the Balkans and Hungary to other countries in the European Union, sometimes paying smugglers to drive them, but the discovery of the bodies in the truck showed there is no truly safe path.

In Austria, officials said they are still investigating but believe the migrants suffocated. Investigators found a Syrian travel document, indicating that at least some of the dead were refugees fleeing violence in Syria.

The 71 included eight women and four children, the youngest a girl between 1 and 2 years old, the others boys aged 8 to 10. Authorities initially estimated the death toll at 20 to 50, but raised it after officials counted the bodies at the warehouse.

Police in Hungary said that as of Tuesday, 776 suspected human smugglers had been detained this year, compared to 593 in all of 2014. Over the last several days, 21 suspected human traffickers — 16 Romanians, two Syrians, two Hungarians and a Russian citizen — had been arrested and 16 vehicles carrying around 100 migrants toward the West had been confiscated, they said.

Volunteers, tending to hundreds of migrants a day in a transit zone set up at Budapest's Keleti train station, asked people to bring candles and flowers to a tribute to be held there Friday evening in memory of the 71 victims.

The truck with the 71 migrants inside was found parked in the safety lane of the highway from Budapest, Hungary, to Vienna on Thursday. It was not clear how long the bodies had been in it.

State prosecutor Johann Fuchs said the perpetrators could be charged with human smuggling, danger to public safety leading to death, or murder.

Two Hungarian police detectives were working with authorities in Austria on the case, said Hungarian national police spokeswoman Viktoria Csiszer-Kovacs.

Austrian Interior Minister Johanna Mikl-Leitner said the tragedy "should serve as a wake-up call ... for joint European action" in dealing with the torrent of migrants flocking to Europe. Melissa Fleming, spokeswoman for the U.N. refugee agency in Geneva called the tragedy "absolutely shocking."

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Jahn reported from Vienna. Associated Press Writer Alison Mutler in Bucharest, Romania; Pablo Gorondi in Budapest, Hungary; and Jamey Keaten in Geneva contributed to this report