(CNN) Four human traffickers have been sentenced to life in prison by a Hungarian court for the deaths of 71 migrants found inside an abandoned truck in Austria, Reuters reported Thursday.

The bodies of the migrants were found by police in August 2015 , decomposing in the heat in the truck on the A4 highway which links Vienna and Budapest, the capitals of Austria and Hungary.

Those who died probably suffocated inside the truck, Austrian authorities said at the time

The Afghan ringleader and three Bulgarian accomplices were handed the sentences by a Hungarian appeals court Thursday. They had been found guilty of manslaughter and given lesser terms last year, Reuters reported.

Ahead of that verdict, the court heard that when the migrants realized they may suffocate, they tried to get the driver's attention by banging on the doors and screaming. According to Reuters, the four traffickers had refused to stop the truck and open the doors to allow air in, despite the pleas from those inside.

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