The 22-year-old man arrested after this weekend’s deadly shooting in Mansfield is now facing gun charges, according to the Bristol County District Attorney’s Office.

William O’Brien, of Manchester-By-The-Sea, was detained on Saturday during the initial investigation into the homicide of 23-year-old Samuel Waters, of Mansfield.

O’Brien has been charged with carrying an illegal firearm and carrying a loaded illegal firearm. He will be arraigned on these charges Monday morning in Attleboro District Court.

Massachusetts State Police detectives assigned to the DA’s office, Homicide Unit prosecutors and Mansfield Police continue to investigate the Saturday morning homicide.

The Southeastern Massachusetts Regional Emergency Communications Center received a 911 call Saturday at 11:11 a.m., reporting a shooting at 42 West Church St.

When first responders arrived on scene, they found Waters, who was already dead.

“There is no reason to believe the public is in any danger,” the DA’s office said in a statement. “The investigation is extremely active at this time and no further information can presently be released.”