Im sure other suspects wouldent have been pursued because the trail by that time would have colder than Moscow in winter.
My personal opinion would be that the Police were under pressure to find the bombers. They nabbed the wrong suspects, and when they realised they had nabbed the wrong suspects they decided to beat and torture a confession out of them anyway given the pressure they were under to find the bombers. Given that their confessions were taken off in them in this way it’s no real wonder that the B6 later retracted those confessions.