BROOKLYN - Investigators are on the hunt for a dangerous police impersonator wanted in an armed home invasion. Police say the man knocked at someone's door in Canarsie yesterday, pretending to be a cop. He had a gun, a police badge and a jacket with NYPD patches on it. Once inside, the man tied up his victims and covered their heads while an accomplice helped him steal cash. Investigators have released a sketch of the impersonator, who's described as a white male in his 40s. Police have not released a description of the second suspect. Anyone with information is urged to call Crime Stoppers at 1-800-577-TIPS.Police are warning residents to call 911 if they are unsure a plainclothes cop is really an officer.