The older of the brothers, Hussein Khalid, 34, was an archaeology graduate student who wanted to reach Germany to complete his doctorate and brought along a younger brother and a family friend. “He is well educated and very careful, and he talked to a lot of people who had made that trip,” Mr. Khalid said. “Everyone agreed: Never get on a truck.”

In Internet-telephone calls home, Hussein told his family that he had insisted on a sturdy “yacht” instead of a raft to cross the Mediterranean from Turkey to Greece, at a premium price of $1,800 per person. He made his way from the boat to Belgrade, Serbia, without the help of any smuggler.

He sent home a photograph of himself lounging with his feet up in a Belgrade bunkhouse where the three men were renting beds for $12 a night, and he left relaxed and confident audio messages for his family weighing whether to hire a smuggler for the final leg of their journey.

They hired one just to be safe, he told his family, to navigate the aggressive border security of the Hungarian police. The family said Hussein paid about $1,800 a person to a smuggler named Karwan el-Sulmani, who promised a passenger car ride all the way to Germany. Hussein had about $4,300 left in his possession when he entered the truck, his brothers said.

More than 20 of the 71 dead migrants came from the oil-rich Kurdistan region of Iraq, a relatively stable and prosperous area that remains a destination for job seekers from India, Pakistan, Africa and elsewhere.

Several families there said that they had made advance payments of as much as $4,500 to a local smuggling agent working with Mr. Sulmani. The agent does business under the name “Jamal Guarantee” — although none of the interviewed families of his dead migrant clients have recovered their initial payments.