The Rev. Al Sharpton will hold a vigil tonight outside police headquarters to support the families of men killed by police, including recent victims Omar Edwards and Shem Walker, as well as Sean Bell, who was killed outside his bachelor party at a Queens strip club in 2006. Sharpton's National Action Network is organizing the vigil. Walker, the most recent victim, was an army veteran who was killed by an undercover cop during a drug sting in Clinton Hill; NYPD sources say the cop had earphones in to keep in touch with his team and didn't hear Walker's demand that he get off his stoop. Cops say Walker kicked the officer in the head and grabbed for his gun in the ensuing scuffle; witnesses insist the cop never identified himself. And in May, Edwards, an officer himself, was killed while chasing a man who had broken into his car. Earlier this month a grand jury declined to indict the officer who fatally shot him.