There has been no investigation of the shooting by the Afghan government nor any mention of it in the press. The F.B.I. questioned Hashmat Karzai a month ago, he acknowledged, but it is not clear whether American investigators are pursuing the matter. An F.B.I. spokesman declined to comment.

Image Waheed Karzai, 18, a relative of Afghanistan's president, was shot to death.

While some family members accuse the Karzai government of stonewalling, they do not claim that the president played an active role in blocking an investigation. Instead, they blame several of his brothers, including Ahmed Wali Karzai, the political boss of Kandahar and southern Afghanistan, for trying to hush up relatives and forestall an official inquiry, perhaps with the president’s knowledge.

“Not a single soul has come to investigate,” Yar Mohammad Karzai, 62, said in a recent telephone interview. “I told one local official, what do you want me to do, knock on Obama’s door?”

Noor Karzai, 40, a cousin who lives in Maryland, expressed similar disappointment. “They are protecting Hashmat,” he said. “He is sitting in Kabul getting money from the U.S. government. No one will touch him. We are sending billions of dollars of U.S. taxpayer money to Afghanistan, and this is how the government operates.”

A spokesman for the Afghan president said that the case was a criminal matter and denied that the president sought to interfere. Reached by telephone on Saturday, Ahmed Wali Karzai declined to comment on the matter, as did officials at the United States Embassy in Kabul.

Frustrated by the seeming inaction on the killing, nearly a dozen family members agreed to be interviewed for this article. Some, including Yar Mohammad Karzai, Sona Karzai and Zalal Karzai, who witnessed aspects of the shooting or its immediate aftermath, also provided documents about the killing. They include a complaint that Yar Mohammad Karzai filed with the Dand district police in Kandahar Province naming Hashmat Karzai as Waheed’s assailant, the boy’s hospital records and a death certificate stating that he died of gunshot wounds.

Other family members, saying they feared retribution, agreed to speak only on the condition of anonymity, as did three witnesses from the Karz mosque. All three said they heard the shooting across the street; one identified Hashmat Karzai as the robed man he saw exiting the house.