The bodies of the 59 men, eight women and four children were already in an advanced state of decomposition when they were found.
In a case that caused widespread revulsion, the bodies of the 59 men, eight women and four children were already in an advanced state of decomposition when they were found.
The defendants are allegedly members of a human-trafficking gang which smuggled more than 1,200 people into western Europe at the height of the continent's 2015 migrant crisis.
According to prosecutors, migrants were "often carried in closed, dark and airless vans unsuitable for passenger transport, in crowded, inhuman, excruciating conditions".
In the fateful transport of August 26, 2015, the migrants banged and shouted that there was no air inside the refrigerated poultry truck they had been crammed into.
But the Afghan gang leader told the two drivers by phone "to ignore the people suffocating and to reach western Europe as soon as possible," according to the charge sheet.
The Afghan, a Bulgarian ringleader and the two drivers, both Bulgarians, were charged this month with homicide "with particularly cruelty" and face life imprisonment.
Seven others face lesser charges and jail. Nine of the suspects -- including the main four -- are in custody in Hungary and one is in Bulgaria, while the 11th is at large.
The migrants were deemed to have suffocated before the vehicle crossed into Austria, so the trial is being held in Hungary.
Szabolcs Sarkozy, a spokesman for the court in the southern Hungarian town of Kecskemet, told AFP that "hopefully" there will be a verdict this year.