BOSTON (CBS) – Boston Mayor Marty Walsh and Police Commissioner William Gross are calling for and end to violence in the city after the shooting of a store clerk in Roxbury.

“I just want to say how frustrated and angry I am right now in dealing with this cruel sense of violence,” Walsh said. “We’ve seen too many of them this summer. We’ve seen too many homicides this summer. We’ve seen too many shootings this summer.”

On Tuesday night, 21-year-old Tanjim Siam was working at the M & R convenience store when an armed man came in and demanded cash and cigarettes. Officers said Siam handed everything over, but the robber shot him in the head.

“The violence in our city needs to stop,” Walsh said. “We need to take responsibility.”

As of Wednesday night, Siam was in a coma at Boston Medical Center. Police are still searching for the suspect.

“A young man from Bangladesh comes here to Boston to seek a better quality of life,” Gross said. “Then a coward, trust me a coward, shoots him during a robbery. Take the money, and leave. Why commit a cowardly like to act like that? That was an innocent young man.”

Gross again called for repeat offenders to be held accountable, citing a shooting three nights earlier.

“The person arrested was arrested with a firearm, had been arrested four days earlier with a firearm, wearing an electronic bracelet that he cut off to commit that shooting again that night,” Gross said. “Are you kidding me?”

The commissioner said communities are not desensitized to violence and have been helping police make arrests.

“I only hope that the judicial process is listening, and we should not be bailing out people putting them on electronic bracelets when they get arrested with firearms,” Gross said. “You’re sending the wrong message.”