Exercise with Three Unknowns

The story

Criminal investigation is investigating the case of robbery of the factory cashier. At the checkpoint of the factory of precision mechanics and optics, two criminals attack the cashier. Criminals manage to escape by the car, waiting for them around the corner. At the scene of the crime, criminal investigation officers arrive Major Dorokhov and Lieutenant Matushkin. They interview witnesses, but they did not remember properly any attackers or machine numbers, but noticed that one prevented the other from firing.