"We have found the source of evil. I mean particular masterminds of both crimes," Fridinsky told a press conference on Monday.
The deputy prosecutor general didn't give any names.
However, the groups who prepared and performed the explosions are not absolutely similar, he stressed. "Some people are involved in both terrorist acts and others are involved in one of them," Fridinsky noted.
A man involved in the September explosion was arrested. He is charged with terrorism and assassination, Fridinsky added. According to him, "the law enforcement bodies have to check and secure many facts".
The explosions in suburban trains occurred in the Stavropol territory in September and December 2003. The first terrorist attack left 6 people killed and 80 injured. The December explosion killed 47 and wounded more than 100 passengers.