A former US student accused of spying on a homosexual encounter involving his room-mate, who later killed himself, has gone on trial in New Jersey. Dharun Ravi, 19, denies 15 charges, including invasion of privacy and bias intimidation, which is a hate crime. Tyler Clementi, 18, jumped to his death from a bridge on 22 September 2010. Prosecutors said Mr Ravi planned to \"expose\" Mr Clementi\'s activity. Defence lawyers called Mr Ravi\'s actions \"stupid\". Early reporting on the case focused on the presumed link between the spying and Mr Clementi\'s death. But evidence of Mr Clementi\'s motivations have not become public and prosecutors have not addressed the issue in their arguments. \'Not harassment\' Prosecuting lawyer Julia McClure told the court during the opening statements that Mr Ravi\'s actions were intended to humiliate his room-mate at Rutgers University. \"They were planned to expose Tyler Clementi\'s sexual orientation and they were planned to expose Tyler Clementi\'s private sexual activity,\" she said. But Mr Ravi\'s lawyer argued that the accused never victimised Mr Clementi and was not a criminal. \"He never transmitted any images. He never harassed his roommate, he never ridiculed his roommate, he never said anything bad about his roommate,\" Steven Altman said. The attention surrounding Mr Clementi\' s death triggered a national debate about tolerance and social acceptance of young gay men. At issue in Mr Ravi\'s trial is what motivated the former student to spy on his room-mate. The most serious charge he faces - bias intimidation - is a hate crime and carries a potential sentence of 10 years in prison. Twitter message Prosecutors described to the court the events of 19 and 21 September 2010, when Mr Clementi asked Mr Ravi if he could have the room to himself. Mr Ravi, who was in a friend\'s room, activated their webcam and saw the two men together, allegedly kissing. Mr Ravi tweeted about what he saw and also posted a message on Twitter when Mr Clementi asked to have the room again, two days later. Ms McClure said: \"These acts were purposeful, intentional, planned. I would suggest to you beyond that, they were mean-spirited, malicious, and criminal.\" Another Rutgers student, Molly Wei, was initially charged, but the case against her was dropped after she agreed to enter a pre-trial intervention programme and co-operate with the prosecution. In December, Mr Ravi turned down the opportunity to negotiate a plea deal that would have spared him jail time.