Investigators opened a criminal case on Monday over an incident near a high-security penal colony in the Chelyabinsk region late last year, when inmates' relatives allegedly attacked OMON riot police officers.
The Investigative Committee said in a statement that unidentified suspects armed with metal pipes, sticks and stones had organized "mass riots" near Kopeisk's prison colony No. 6 on the night of Nov. 24.
The statement said the clashes disrupted prison officials' work and that riot police officers were injured in the violence, which took place as hundreds of inmates revolted over alleged inhumane treatment and extortion within the prison's walls.
In the aftermath of the prisoners' revolt, President Vladimir Putin fired Alexei Velichko, deputy head of the Federal Prison Service. Twelve other prison officials were punished after more than 350 official complaints were filed with local investigators citing gross mistreatment by Kopeisk prison staff.
On Nov. 27, investigators opened five criminal cases against another set of unidentified suspects on charges of physically harming law enforcement officers over the same clashes outside the confines of the prison. The suspects each face up to five years in prison on those charges.
The latest charges, of organizing and taking part in mass riots, carry a maximum sentence of 10 years' behind bars.