Saying the accused killer used his girlfriend’s hammer to beat his cousin to death before disposing of his body in the Collins River, the murder trial began Tuesday against Chad Thompson, who is accused of killing Tracy Martin.“The name of the defendant’s girlfriend is on the hammer,” revealed District Attorney General Lisa Zavogiannis during opening statements. Zavogiannis said the hammer prosecutors believe Thompson used to inflict the fatal blows had the name “NINA” inscribed on it for Nina Parker.The hammer, the district attorney told the jury, was found next to the home of one of Thompson’s friends, the same friend who prosecutors say he tried to enlist to help rob his cousin of his Social Security money.Prosecutors say there were two wounds on the back of Martin’s head when he was found by fishermen in November 2011. The victim’s upper torso was submerged in the river as if he had been tossed from atop the steep embankment which overlooks the confluence of the Collins River and Charles Creek.