A national police statement said the Bulgarian national was arrested on Saturday evening. Police said Sunday they will seek to have him held in custody on suspicion of human trafficking.
On Saturday, a court in the central city of Kecskemet — from where prosecutors say the truck departed — placed four other suspects under preliminary arrest pending possible indictment.
Those men, three Bulgarians and an Afghan, were arrested Thursday in southern Hungary. The truck with the dead migrants was found earlier that day parked along the Budapest-to-Vienna highway.
Austrian experts are performing autopsies on the victims: 59 men, eight women and four children.