Common robbery and specialized robbery

Three of the fifteen convenience stores in your community have been robbed within the last month, all between 11:00 p.m. and midnight. The suspect, who was captured on security videotape in two of the robberies but wears a ski mask over his face, is apparently responsible for the robberies. His modus operandi is to enter the store when it is empty, point a gun (revolver) at the clerk, and demand all the money in the cash register. The suspect speaks with a stutter and had difficulty speaking during one of the robberies. The clerks all said they smelled alcohol on the suspect.
What criminal investigation actions should be taken?
What considerations should be noted for the perpetrator and the victims?
Is this case solvable? Should it be pursued? Why or why not?