Jurors learned those details Tuesday during the testimony of Gary Charydczak, a detective in the Middlesex County Prosecutor's Office who testified in the roommate's criminal trial. The detective said he learned about Clementi's computer use from examining the hard drive of the laptop that was found in his Rutgers University dorm room.
He displayed the Tweets that he said were saved to Clementi's hard drive under the names "untitled.jpg" and "secondtime.jpg."
Twenty-year-old Dharun Ravi faces 15 counts including bias intimidation and invasion of privacy against Clementi, who jumped to his death from the George Washington Bridge on Sept. 22, 2010, one day after authorities say Ravi attempted to spy on him.
Prosecutors say Ravi used Twitter first to tell followers that he had seen his roommate "making out with a dude" on Sept. 19, and two days later to "dare" them to video chat him when Clementi had again asked to have the room to himself so he could have a guest over.
Authorities also say Ravi told friends about the expected dorm-room liaison through other means, including text messages. During testimony Monday, jurors were shown texts he sent to a friend from high school who was then attending Cornell University.
In one part of the exchange, the friend, Michelle Huang, texted Ravi: "Watch out, he may come for you when you're sleeping."
Ravi responded that he had his computer set to alert him if anyone was in his bed when he wasn't there. "It keeps the gays away," he said.
The exchange may help prosecutors show that Ravi had malice toward gays - a necessary element to persuade jurors to convict Ravi on the bias intimidation charges he faces. But he and his friend went on to talk about some of their gay friends.
In testimony earlier Tuesday, Rutgers computer system manager Timothy Hayes told jurors it appears Ravi's computer was used in two video chats on Sept. 21, 2010.
That doesn't prove that Ravi spied on his roommate, but it may bolster the prosecution's case that he was preparing to attempt to spy on Clementi that night. Clementi committed suicide a day later.
Authorities say Ravi used his webcam to see his roommate and another man kissing on Sept. 19 and viewed it from the room across the hall from his own.
Hayes told jurors that the data the university collected was not able to show online interactions between two computers on the same wing of the dorm. But Charydczak testified that the computers of both Ravi and another dorm resident, Molly Wei, had a record of a video chat Sept. 19 at about the time she said that they briefly used it to see Clementi and the other man kissing.
Prosecutors also have been building the case that Ravi went to the rooms of dorm mates that evening to test his webcam.
They tried to use Hayes' testimony to corroborate that. He said there was a web chat between his computer and Lokesh Ojha's at 6:58 p.m. that evening, and another with Alissa Agarwal starting 46 minutes later. Both those students testified that Ravi showed them how they could use a web chat program to see what was happening in his room.
There has been no evidence that anyone used a videochat service to spy on Clementi that night.
Court documents suggest that Ravi's computer was unplugged before his guest arrived.
Hayes said it seems that Ravi's computer was unplugged for about two hours that night, beginning at 9:25 p.m.
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