An 18-year-old San Bernardino County man was charged Monday with murder in connection with the shooting death of a man in Long Beach last December. The murder charge against Mario Amarion Jennings of Rancho Cucamonga includes allegations that he personally and intentionally discharged a handgun and that the crime was committed for the benefit of, at the direction of, and in association with a criminal street gang with the specific intent to promote, further and assist in criminal conduct by gang members…