The man testified that he had met Tyler Clementi in August 2010 through a social-networking site for gay men and said he texted repeatedly after their third and final rendezvous. He wanted to see Clementi again, M.B. said, but didn't know the college freshman's last name.
"I didn't know it until I picked up a newspaper," M.B. said.
Clementi's name was not in the paper until about a week later, when it was reported that he had jumped to his death from the George Washington Bridge.
They had chatted online initially, M.B. said, and their first in-person meeting was in Clementi's dorm room Sept. 17 - two days before the alleged spying.
The man's testimony came in the trial of Clementi's roommate, Dharun Ravi, who is charged with bias intimidation, invasion of privacy, and other crimes.
The judge did not allow photographs of M.B. to be taken in the courthouse, barred audio or video of him to be recorded, and said he would be identified in court only by his initials. The man's lawyer successfully fought to conceal M.B.'s identity because he is considered a victim of an alleged sex crime. Invasion of privacy is classified as a sex crime in New Jersey.
Jurors were given his whole name to make sure none knew him.
On Friday, the trim young man appeared in court in a button-down shirt. He did not match the description of the overweight "sketchy" or "homeless"-looking man students had reported seeing visit Clementi. His hair was closely cropped, and he did not have the goatee some described him as having.
Because of the secrecy surrounding the man's identity, there was an unusually large media contingent packed into the Middlesex County Courthouse for what was already a high-profile trial.
After a full day's testimony - most of it during testy cross-examination by a defense layer - many mysteries remained. M.B. said he was 32. He disclosed little else on his own. In an apparent oversight, jurors were shown a picture of Clementi's cellphone, which revealed the name he entered for him: "Mike Nice."
His lawyer, Richard Pompelio of the New Jersey Crime Victims' Law Center, said he did not believe M.B. was married and did not know whether he was out as a gay man.
"He's a fine young man who came here under horrible circumstances to tell the truth," Pompelio said outside the courtroom during a break in testimony.
He said M.B. had a fledgling relationship with Clementi and learned about his death from hearing it on the radio.
In court, M.B. himself said he lived about a 20-minute drive from Clementi's dorm and was starting a new job Sept. 20, 2010.
He testified that he met Clementi in his dorm room three times. The first was on Sept. 17, when he said Ravi was not expected home until the middle of the night. He said he was careful to leave before Ravi was due back.
"I made sure to leave well before 2 a.m. as to not cause any conflict," he said.
The second was Sept. 19, the date of the alleged spying - and the time he said he noticed the webcam.
He said he and Clementi were naked and had sex that night. People who saw webcam images of his encounter with Clementi have testified that they saw no more than a few seconds of video and that the men were only seen kissing. At one point, some said, their shirts were off, but their pants were on.
The man told jurors that there were about five students looking at him as he left the building Sept. 19.
"Had they been in the street or somewhere other than this building, I would have asked them why they were looking at me," he said. He called their actions "unsettling."
Ravi's defense lawyer, Steven Altman, repeatedly asked M.B. whether he wanted to meet Clementi for a movie or a coffee - or go anywhere besides the dorm.
"I preferred just to wait until we could have the privacy of a room, wherever that room might be," M.B. said.
His home often would not work, he said.
The third time he met Clementi was two days later, when Ravi is charged with attempted invasion of privacy. There has been testimony that the webcam feed did not work that night. According to court papers filed previously, it was unplugged.
M.B. testified that he heard comments from the courtyard outside the dorm that night that bothered him. But he was not allowed to say what they were.
He testified that he had wanted to see Clementi again.
"As far as whether I was going to return to that building to see him, I felt a little uneasy about it," he said.
Ravi faces 15 criminal counts. The most serious is bias intimidation, a hate crime punishable by up to 10 years in prison.
Much of the testimony so far has come from students. Several said Ravi told them that he had used a webcam to see what was happening in the room, but none said Ravi had general malice toward gays.