TAMPA — Members of the improv comedy group knew the unspoken arrangement: Go along with the persistent sexual advances from the USF instructor who led their club and get special treatment.

Now a University of South Florida Title IX investigation has concluded that, under school policy, former adjunct Nicholas Riggs sexually assaulted one student and sexually harassed at least one other, abusing his position to coerce them. One student called him a "puppet master."

Riggs and his wife, Hannah Prince, then a graduate student, often approached students together, the report found. Over time, consensual sex became murkier as students — male and female — felt manipulated and intimidated under the pressure of Riggs' advances.

UPDATE: USF improv instructor responds to sexual misconduct filing

The Tampa Bay Times recently obtained the 38-page report, compiled for USF this spring by an outside attorney, Mariah Passarelli of Buchanan Ingersoll & Rooney PC.

In it, Riggs, 31, denied having sex with any USF student besides his wife, who was his student when they met. Reached by phone, he declined to respond to the allegations.

"It's a sensitive issue, and there's a lot of things that have been said in all directions," he said. "I just don't know what to say. These things get pulled out of context quite a bit."

[SCOTT KEELER | Times]

The Spitfire Theater at 14 18th Street S in St. Petersburg, is run by former USF adjunct professor Nicholas Riggs. Riggs was found to have sexually assaulted and harassed USF students in his improv group, according to a Title IX investigation by the school.

Barred from teaching at USF, Riggs now runs Spitfire Theater, a small improv comedy venue in St. Petersburg, with his wife. He has also stopped teaching at the University of Tampa, St. Petersburg College, Hillsborough Community College and Florida Southern University. Prince, 25, did not respond to requests for comment.

USF officials said a larger investigation into Riggs' actions continues. A memo from USF's office of diversity, inclusion and equal opportunity said Riggs should be banned from stepping foot on any USF campus.

"As soon as USF became aware of the allegations against Riggs, we immediately began to review the matter," spokesman Adam Freeman said in a statement. "USF values respectful and fair treatment of all members of our community."

For one of Riggs' victims, Passarelli wrote, the harassment "was severe and pervasive enough to have created a sexually hostile education environment. … Under this level of coercion, intimidation and/or duress by Riggs, I do not believe that (the victim) could have given valid sexual consent."

• • •

The first complaint about Riggs came in December 2016, signed a "Concerned (and Angry!) Parent."

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Days later, a male student filed another complaint, mirroring the first. Passarelli couldn't decisively link them, but they cover the same ground.

The parent said that by 2014, their son's second year doing improv at USF, he became "more withdrawn, and actually angry about being part of the group." Then in 2015, he told the parent he'd had sex with Riggs and Prince together, which he said was a common occurrence in the club.

Technically, Riggs and Prince worked with two groups. Improv@USF was a university organization, and Post Dinner Conversations was not. But the groups were intertwined, and Riggs "picked his favorites" for PDC, the student told Passarelli.

After performances, the student said, Riggs and Prince invited students over for drinks, maybe some marijuana. Guests would talk, play video games and dance until the early hours, sometimes staying overnight.

It became clear that being in Riggs' good graces was key to getting the chance to perform, the student said. Students "who weren't good enough to him or weren't sexy enough to him had to sit and watch," he said.

The student became entangled with the couple in 2014, when he learned they had an open relationship, he said. He confessed to Prince his fear that he'd leave college a virgin, and Prince performed oral sex on him, he said.

In this image taken from Facebook, Nicholas Riggs is seen with his wife, Hannah Prince. The two figure prominently in a report that details a Title IX investigation by the University of South Florida.

"I hear you fooled around with Hannah," Riggs later said, the student recalled. "Do you think you'd ever do it with a guy?"

Saying no might mean losing the chance to be intimate with Prince again, the student feared, so he performed oral sex on Riggs.

From there, the sexual encounters kept coming, the student said, but only with Riggs. He felt like the couple had "pulled a bait-and-switch." Riggs found ways to isolate him, the student said, giving him marijuana and alcohol and pressuring him into oral sex.

Each time, the student told himself "this would be the last time." He would close his eyes, "trying to imagine that it was anybody else."

"I think it would be best for your sake if you didn't tell anybody about this," Riggs told him, the student recalled. Or when the student would resist doing more sexually, he recalled Riggs saying, "Don't you hate it when somebody says no but you know they want to say yes?"

The student said that, around friends, Riggs would humiliate him for being a virgin.

When the student put an end to the sex acts, Riggs and Prince shut him out of parties and performances, he said. From there, his improv world collapsed.

In her report, Passarelli said the consensual relationship broke down because of Riggs' intimidating behavior.

She called it sexual assault.

• • •

While Passarelli interviewed witnesses, one decided to file a complaint of her own.

Riggs was this student's professor in 2014. She thought he was brilliant and stayed after class to talk improv. Riggs wrote, "I love your mind" on her final exam.

That summer, the student went to the beach with the improv club. She told Riggs she liked his class, and he responded, saying he "had a really big crush" on her, the student told the attorney.

"Do you think Hannah is pretty?" Riggs asked, the student recalled. "Do you want to have sex with both of us?"

She went into their house, where she, Riggs and Prince drank wine and smoked marijuana, she said, then began to engage in sex acts.

The trio repeated the encounter three or four times. Meanwhile, the student said, she and Riggs developed a sexual relationship of their own for the next nine months.

Home for winter break in 2014, the student decided she wanted to stop having sex with Riggs, even though she feared losing her spot on improv tours.

Riggs came over after she broke the news, she said, and they had sex, even though she told him she didn't want to.

"You should know better, you're 30 years old," she said she told him. "I'm your student, this isn't fair."

Again, Passarelli concluded that the relationship began with consent. She looked at romantic texts between the two. But, she wrote, Riggs' visit to the student's apartment amounted to sexual harassment.

• • •

Passarelli also talked to a student who said Riggs and Prince had felt like a brother and sister. But he said Riggs kept making him uncomfortable.

While watching a movie, Riggs would massage the student's feet, moving up his legs, the student said. In Riggs' car, he said, he would have to remove Riggs' hand to make the touching stop.

One night at the couple's house, Prince insisted he sleep in their bed. There, Riggs started touching the student's arm, he said. The student bolted out. Down the street, he pulled over to throw up, shaken and scared.

[SCOTT KEELER | Times]

Messages on the front window at the Spitfire Theater invite people to attend shows, participate in classes and perform. The theater is run by former USF adjunct professor Nicholas Riggs. Riggs was found to have sexually assaulted and harassed USF students in his improv group, according to a Title IX investigation by the school.

The report also found that Riggs failed to report a sexual assault at one of his parties, though a student told him that she awoke to find a male roommate of Riggs groping her.

Elsewhere, the report hints at the nature of the larger investigation into Riggs' time at USF.

Questions arose about Riggs' academic integrity, particularly possible misrepresentation of research when it came to his dissertation, which no longer appears on USF's website.

His work followed four couples in the improv group, including himself and Prince, as they performed and discussed improv. Riggs wrote in his paper that his study "was exempted" from Institutional Review Board approval for using human subjects. A witness in the report suggests that Riggs may not have gotten the consent of the couples he studied.

Passarelli said the dissertation "is reflective of Riggs' manipulation and control over others."

"My experiences with romantic relationships and with theater have always gone hand-in-hand," Riggs wrote in his paper, "probably because I've always found it easier to talk to love interests in private after they watch me express myself in public."

• • •

The report, which cost USF about $20,000, said Prince was separately investigated under Title IX. USF could not confirm that report's existence because of student privacy laws.

Passarelli, who is based in Pittsburgh, found in her report that Riggs' explanations were not believable. He contradicted himself by claiming he was only "lightly involved" with PDC and that he didn't attend many PDC parties, she wrote. Halfway through her interview with him, he said he had to leave for work and later refused to talk.

A check of state and local records found no criminal charges against Riggs or Prince. Spokespersons at the other area schools where Riggs has worked as an instructor said no issues have been raised about his performance.

Riggs, an Ohio native, came to USF as a master's student in 2009 and started teaching soon after that. He earned a PhD in 2016 and stayed on as an adjunct professor. He last taught in December. He is still listed as a grad student on USF's website.

Times news researcher Caryn Baird contributed to this report. Contact Claire McNeill at (727) 893-8321 or cmcneill@tampabay.com.