A former U.S.A.I.D. worker described the area as a place where the American military and development officers had no idea whom they were dealing with. “The Haqqanis were out there, HIG, Al Haq, ISI,” the worker said, rattling off a host of insurgent groups and the Pakistani intelligence agency, which maintains ties to many of them. “Everyone was there, and the local population is as likely to sabotage a project as to protect it.”

Indeed, some suspected Mr. Arafat of arranging attacks himself. However, they were reported up the American military chain of command like almost all other attacks, without any hint that they might have been staged for the purpose of squeezing money from the United States government.

In one instance in 2009, Afghan soldiers searched a small car in Gardez and found it filled with explosives, and the two men riding in it quickly explained that they worked for Mr. Arafat. The explosives disappeared and the men were freed before they could be handed over to the United States military, according to an American official familiar with the case.

Another American contractor said that an Afghan worker had told him that he had been ordered by security subcontractors to write “night letters” — anonymous death threats — to the Americans working on the highway to frighten them into paying more for security.

Shootings and other violence often broke out on paydays, said one American official who worked on the road, adding that those were the only occasions when many of the local security guards would show up, even though on paper there were supposed to be nearly 1,000 guards.

“On paper, the G.K. road was paying an enormous security detail of local-hire Afghans,” said one United States official. The highway contractors “would make a big deal out of their camps’ getting hit from time to time, and some of their guys would get shot in night attacks, but every instance I ever heard about coincided with payment negotiations with the Afghan security detail, of whom Arafat was the chief point of contact,” the official said.

It is impossible to determine how many of the attacks on the highway may have been staged by Mr. Arafat or his men. Despite all the money spent on security, however, there have been 364 attacks on the Gardez-Khost Highway, including 108 roadside bombs, resulting in the deaths of 19 people, almost all of them local Afghan workers.