Protesters stormed the government building Tuesday in a volatile southern Russian region amid rising anger over a multiple slaying that led to the detention of the regional president's son-in-law, police said.

About 2,000 people, including elderly women in head scarves, smashed metal barriers against the building's doors, shattering the glass panels, according to video shown on Russian state television.

The crowd then pried open the doors and entered the building, seizing the office of Karachayevo-Cherkessiya (search) President Mustafa Batdyev (search), the region's Interior Ministry said.

The NTV television channel said Batdyev fled through a back door. Regional police said that no officials had been in the building at the time of the protest.

At least seven police were injured in the clash, the Interior Ministry said. Some special forces troops sent inside to prevent protesters from seizing the entire building also were injured.

At least two civilians also were hurt, the Interfax news agency reported.

The protest began after prosecutors said they had discovered a common grave that appeared to contain fragments of the men's bodies.

Relatives of the victims say the men disappeared Oct. 10 after being summoned to a meeting at a cottage belonging to Ali Kaitov (search), Batdyev's son-in-law. Investigators found bullet casings and bullet holes in a search of the cottage. Neighbors also reported hearing automatic gunfire.

Kaitov surrendered Oct. 25 and is detained on abduction and murder charges, which he denied. Two more suspects were detained in St. Petersburg over the weekend, and Russian media said they provided information about where the bodies were located.

The Russian prosecutor-general's office said the bodies apparently had been sprayed with gasoline and set ablaze, ITAR-Tass reported.

Prosecutors earlier arrested four police officers and three security guards on charges of involvement in the abduction.

The Karachayevo-Cherkessiya region has been plagued by frequent contract murders and other violence, some linked to rivalry between local criminal clans and some spilling over from warring Chechnya.