Some attribute responsibility for the kidnapping and murder to the leftist anti-Pashtun group Settam-e-Melli, but others consider that to be dubious, pointing to a former Kabul policeman who has claimed that at least one kidnapper was part of the Parcham faction of the People's Democratic Party of Afghanistan. Disinformation that was spread in the Soviet and Afghan press after the murder blamed the incident on the CIA, Hafizullah Amin, or both. Anthony Arnold suggested that "it was obvious that only one power… would benefit from the murder—the Soviet Union," as the death of the ambassador "irrevocably poisoned" the U.S.–Afghan relationship, "leaving the USSR with a monopoly of great power influence over" the Nur Muhammad Taraki government. Carter's national security adviser Zbigniew Brzezinski stated that Dubs' death "was a tragic event which involved either Soviet ineptitude or collusion", while the Afghan handling of the incident was "inept." The Taraki government refused U.S. requests for an investigation into the death.