Opening arguments were heard Friday in the trial involving the former Mount Kisco officer accused of causing the death of a homeless illegal immigrant.The illegal immigrant, Rene Perez, was found near death lying on the side of Byram Lake Road last April. The Perez family says former police officer George Bubaris caused the fatal blow that killed the drunken illegal immigrant.Bubaris, 31, could go to prison for manslaughter if found guilty of killing Perez. Bubaris? attorney, Andrew Quinn, says Perez had a long history of being highly intoxicated, falling and getting injured. He maintains Bubaris did not cause Perez?s death.The first witness called to the stand Friday was North Castle Police Sgt. James Thomas, who administered first aid to Perez. Thomas says the victim had blood on his sweatshirt and his breath smelled of alcohol.The trial will resume on May 27.Trial begins for ex-cop accused in fatal beating