Who killed McCall's wife in Equalizer?

Could you please elaborate on the mystery surrounding the murder of McCall's wife in the film "The Equalizer"? Who was the perpetrator behind this heinous crime, and what drove them to commit such a brutal act? Did McCall's past as a former government operative have anything to do with it? Or was it a random act of violence that caught him and his wife in its crosshairs? We need to uncover the truth behind this tragic event and bring justice to the victim's family.