A former beat cop who brutalized a prisoner in New York in a grimy precinct bathroom has been sentenced to 30 years behind bars, a punishment his victim calls a clear message that no one is above the law. Justin Volpe fought back tears during the two-and-a-half-hour hearing yesterday in federal court. Reading from a handwritten statement, he apologized to his victim, Abner Louima. Volpe rammed a broomstick into Louima’s rectum in a police station bathroom in 1997 after arresting and handcuffing the 30-year-old security guard. Police said Volpe mistakenly thought Louima had punched him from behind during an earlier melee outside a Brooklyn nightclub. Louima, who addressed the court during the sentencing, did not ask the judge for any specific punishment, although prosecutors had pushed for a life sentence.