A Russian human rights activist has been found dead in a sand pit weeks after he went missing, according to police and a colleague who said Wednesday that he suspects the prisoners' rights advocate was murdered.

The news of Andrei Kulagin's death came a week after the abduction and killing of Natalya Estemirova, a well-respected human rights activist and critic of the Kremlin-backed leader of Russia's war-scarred Chechnya region. Her killing sparked international outrage and underscored the dangers faced by Russians who challenge authorities.

Kulagin was head the Karelia regional branch of the rights organization Spravedlivost, which means Justice.

He was last seen alive on May 14 leaving his home after receiving a phone call from somebody who wanted to meet with him, the organization's director, Andrei Stolbunov, said in a statement on its Web site.

Kulagin's body was found on July 10 in a sand pit on the outskirts of Petrozavodsk, capital of the Karelia region in northwestern Russia, Stolbunov told Ekho Moskvy radio. According to the Interfax news agency, provincial police confirmed Kulagin's body was found in the pit that day, but gave no other information.

"There is no doubt that (Kulagin) was murdered," Interfax quoted Stolbunov as saying.

According to Ekho Moskvy, Stolbunov said Kulagin's family did want his death publicized before the funeral last weekend. He is survived by a wife and a daughter.

Stolbunov said in the Web site statement that Kulagin had fought for the humane treatment of prisoners and worked closely with prison and jail officials in Karelia.

But he said his organization has been subjected to pressure and threats by authorities. "Now they are also killing our comrades," Stolbunov said in the statement.

Rights activists across Russia face bureaucratic barriers, harassment and violent attacks.

Estemirova's July 15 slaying followed the killings of two other Russians who challenged the government over abuses in Chechnya — human rights lawyer Stanislav Markelov, gunned down on a Moscow street in January, and investigative journalist Anna Politkovskaya, shot dead in 2006.

On Monday, police raided the office of a rights group in the Tatarstan region, confiscating computers and detaining the director.

The Kremlin said Monday that President Dmitry Medvedev signed legislation easing bureaucratic hurdles for human rights groups and other non-governmental organizations.

The legislation is one of the few palpable signs of change in the Kremlin's treatment of independent organizations since Medvedev succeeded Vladimir Putin as president. Putin had portrayed rights groups as a potentially dangerous channels for foreign-funded efforts to weaken Russia.

But activists say the law applies only to a limited number of groups, and that internationally funded organizations continue to be viewed with suspicion.