The suicide bomber who killed the Afghan leader responsible for brokering a deal with insurgents gained access to him after delivering an audio recording that the assassin said contained a message from Taliban leaders, President Hamid Karzai said Thursday.

The message was convincing enough that top officials, including Karzai, urged Burhanuddin Rabbani, a former Afghan president, to return to Kabul from a trip abroad because the supposed Taliban envoy said he had a second, important audio recording that could be delivered only to Rabbani.

Ryan C. Crocker, the U.S. ambassador in Kabul, said Thursday that the assassination “raised very serious questions about whether the Taliban and those who support them have any real interest in reconciliation.”

Crocker said Rabbani’s killing in a suicide bombing on Tuesday made this a “sad time, but not a time for despair.”

Crocker’s remarks came as the Afghan government began providing more details about the brazen attack that has dramatically dimmed the prospect of a negotiated end to the 10-year-old Afghan war just as the NATO coalition is starting to disengage.

At the urging of Afghan intelligence officials, Rahmatullah Wahidyar, the member of the High Peace Council who brought the suicide bomber to Rabbani’s home, held a news conference to explain how the killer gained their trust.

Wahidyar, who was wounded in the attack, said the suicide bomber, who went by the name Esmatullah, told council members that he had been sent by Mullah Hamidullah, a purported Taliban envoy. Members of the council, the peacemaking body Rabbani was appointed to lead last year, had held several meetings in Kabul with Hamidullah, Wahidyar said. Those encounters had left council members convinced that Taliban leaders were open to the possibility of a negotiated settlement.

Esmatullah brought with him two audio recordings on a flash drive that he said were made by members of the Quetta Shura, the Taliban’s top leaders, based in Pakistan, Wahidyar said.

“When we heard the message, it was also saying that there were two messages, one for the council and one special message for the professor,” Wahidyar said, referring to Rabbani.

The messages appear to have been credible enough to lead senior members of the council to believe Taliban leaders wanted to discuss peace, despite the group’s public position that it will not negotiate while foreign troops remain in Afghanistan.

“Everyone was desperate to reach out to the Taliban,” said Haroun Mir, a political analyst in Kabul. “Everyone was fooled, even President Karzai.”

Karzai said he heard one of the audio recordings before traveling to New York this week for the U.N. General Assembly session.

A Taliban spokesman has said the group is investigating the killing and has not yet taken responsibility for carrying out the attack.

Hamid Elmi, a spokesman for Karzai, said the country’s intelligence service has evidence suggesting the Taliban “had a hand in this.” He added, however, that “we do not know which faction” of the militant group carried out the attack.

Mir said he doubted that the leadership of the Taliban orchestrated the killing, because the group would have a hard time justifying the slaying of a respected religious leader.

Mir said he did not rule out that a faction of the Taliban adamantly opposed to talks with the U.S.-backed government carried it out. He said, however, that it seemed unlikely that the Haqqani network, an elite militant network aligned with the Taliban, ordered the killing.

U.S. officials say the Haqqani network has ties to the Pakistani government, and they have publicly called on Islamabad to rein in the insurgent group after several spectacular attacks in Kabul.

Meanwhile, NATO officials said Thursday that coalition forces on Tuesday had killed the suspected mastermind of the downing of a Chinook helicopter last month. The incident was the deadliest attack on U.S. troops since the war began.

Military officials said the suspected Taliban leader, Qari Tahir, was killed in an airstrike targeting a dry riverbed in Wardak province. Thirty U.S. troops died in the Aug. 6 attack.

Special correspondent Sayed Salahuddin contributed to this report.