A year after a human rights worker, Natalia Estemirova, was abducted outside her home in Chechnya and found dead beside a highway, the Russian president, Dmitri A. Medvedev, said the authorities had identified her killer and were searching for the person who ordered her murder.
Mr. Medvedev did not offer details, but investigators claim Ms. Estemirova was killed by an antigovernment militant in retaliation for her research into his group, according to an internal document made public this week.
Ms. Estemirova's colleagues and relatives rejected this explanation on Thursday, urging authorities to investigate the theory they have put forward — that she was killed by forces linked to the Chechen government that were unhappy with her inquiries into police abuses.
“We're asking Mr. Medvedev openly: What has been done to look into the theory of possible official involvement?” said Tanya Lokshina, deputy director of the Moscow office of Human Rights Watch. “We are asking the Russian government for concrete information.”
Much of Ms. Estemirova's work focused on kidnapping and other abuses she believed had been carried out under the authority of the Chechen president, Ramzan A. Kadyrov, who has enjoyed unwavering support from the Kremlin. Beginning hours after her disappearance, her colleagues said they believed that Mr. Kadyrov, or forces linked to him, were responsible.
But Mr. Medvedev immediately dismissed theories that implicated Mr. Kadyrov, calling them “primitive,” and Mr. Kadyrov angrily denied any role in Ms. Estemirova's death.
The official investigation has evidently gone in another direction. Roman Karpinsky, a lawyer representing Ms. Estemirova's sister, Svetlana, said the government's primary suspect is a member of a militant group, Akhazur Bashayev — who was reported killed during a counterterrorism raid last fall.
An internal investigative report obtained and published by Novaya Gazeta, the opposition newspaper Ms. Estemirova worked for, also confirmed that investigators were focusing on Mr. Bashayev as the sole named suspect.
According to the account, police found the murder weapon lying next to an identification document with Mr. Bashayev's picture on it, and local people told investigators Ms. Estemirova had been in his village in April, gathering information about the militant group.
Mr. Karpinsky, however, said he was “very skeptical” that Mr. Bashayev was the culprit.
“It seems to me there are more convincing theories which demand meticulous investigation,” he said, noting that Ms. Estemirova's closest associates were convinced that she was killed because she was looking into a public execution carried out last July 7 by the local police. Her inquiries, he said, “aroused dissatisfaction among Chechen officials.”
“We consider that this theory should be, at minimum, checked out,” he said.
Mr. Medvedev, who was meeting with the German chancellor, Angela Merkel, in Yekaterinberg on Thursday, is under international pressure to solve Ms. Estemirova's murder. Amnesty International said the inquiry's slow pace “raises concerns that there is no political will to identify the perpetrators,” and the Council of Europe's human rights commissioner, Thomas Hammarberg, called the lack of any arrest “unacceptable.”
Mr. Medvedev defended Russia's efforts, saying it was “false to say that there is no investigation.”
“We have established and positively identified the perpetrator of this murder — the killer,” he said. “Now we have undertaken an investigation to find not only the killer, who is already the target of a manhunt, but also the person who ordered this grave crime.”
Ms. Estemirova's colleagues at the human rights group Memorial responded warily.
“If it is a reference to the police theory, I am very disappointed,” Oleg P. Orlov, the group's head, told the Interfax news service. “That is an extremely dubious theory, but it is very convenient for the authorities.”