(AP) -- With the story of alleged invasion of privacy and bias intimidation already told, prosecutors have turned to trying to show jurors that a former Rutgers University student accused of using a webcam to spy on his roommate's intimate encounter with another man tried to cover up his actions.
A detective told jurors Wednesday that Dharun Ravi sent a pair of Twitter messages on Sept. 22, 2010, after it was believed that his roommate, Tyler Clementi, had killed himself.
One read: "Roommate asked for room again. It's happening again. People with ichat, don't you dare videochat me from 9 to 12." The next: "Everyone ignore the last tweet. Stupid drafts."
Jurors already have heard from a string of witnesses that Ravi sent a similar message a day earlier, but instead of saying "Don't you dare videochat me," it told followers, "I dare you to videochat me."
That message is central to the prosecution's case that Ravi attempted to spy on Clementi on Sept. 21 and intimidated him by telling other people to watch.
The later messages are part of prosecutors' contention that he used Twitter, among other means, to cover his tracks by erasing an earlier message, replacing it with a similar but less damaging one, then claiming it was a mistake.
Ravi, now 20, faces 15 criminal charges including bias intimidation, invasion of privacy and several counts related to the alleged cover-up, including tampering with evidence and a witness and hindering apprehension.
He is not charged in the death of Clementi, who jumped off the George Washington Bridge.
On the witness stand on Wednesday, the ninth day of testimony in the case, Robert Torrisi, a detective at the Middlesex County Prosecutor's Office, testified about what he found on the cellphones of Ravi and some of his friends.
His testimony came a day after another investigator told jurors about Clementi's Twitter use, including that he visited Ravi's page on the social media network 38 times in the two days before he killed himself - and saved screen shots of two messages. In the first, on Sept. 19, Ravi wrote about turning on his webcam from a friend's room. "I saw him making out with a dude. Yay," it concluded. The second one he saved was from Sept. 21. It was the one "daring" people to initiate webchats with him that night.
In addition to the Twitter scrutiny, the investigator compared text messages on the phones. There were some exchanges that remained on friends' phones but were deleted from Ravi's.
Throughout the trial, Ravi's defense attorney has asked students whether Ravi told them to delete data. Most have said no.
Explore further: Expert: Webcam spy suspect's computer used in chat