Southwick, a senior who was sent home Friday by interim head coach Bob Gregory shortly after the team arrived in Hawaii, took a polygraph test after arriving in Boise in his bid to prove his innocence, KTVB reported Sunday.
Initially, Southwick and backup quarterback Nick Patti were suspended for violating team rules, with BSU not providing details of what happened. Eventually, Patti was reinstated, but Southwick was taken to the airport where he says he waited nine hours before his flight.
The incident - and Southwick's denial of involvement - represents a challenge for a program that was already in transition: Former head coach Chris Petersen quit and took a job at the University of Washington earlier this month following an 8-4 season, his worst since taking over as head coach in 2006. Brian Harsin, the former head coach at Arkansas State, has been hired to replace Petersen, but the Hawaii Bowl was seen as a chance for Gregory to elevate his profile.
"It's really important for myself and my family to get this cleared up," Southwick said. "There was no process to properly adjudicate what happened. It's really disappointing that it had to come to this.
Southwick said the results of the polygraph indicate he was telling the truth: He witnessed another player urinate off the balcony, but didn't do it himself.
"Really, this gives me a leg to stand on," he said of the polygraph, adding he went to bed after watching the incident, and learned the next morning at the team's breakfast that he'd been accused.
Max Corbet, the sports information director who was in Hawaii with the team, said in an email that the issue was investigated at the time and a decision was made.
"We investigated the matter with university administrators, coaching staff, a law enforcement official, hotel security and student-athletes," Corbet said in a statement. "We made the decision to send the student-athlete home, and we stand by this difficult decision."
There will be no further comment from Boise State, he said.
Southwick, who described the evening preceding the incident that led to his dismissal as one fueled by alcohol but didn't say if he'd been drinking, declined during the television interview to name the player he says urinated from the hotel balcony.
He said at least three other players testified against him; he maintained his innocence throughout, but coaches decided he should be dismissed, he told the TV station. Southwick acknowledged losing his temper after being accused. "They had to make a call, very quickly," Southwick said. "Unfortunately, they made the wrong one."
He said he tried to contact Boise State administrators while waiting at the airport, but to no avail.
The dismissal puts an end to a difficult season for Southwick.
He missed most of five of the final six Bronco games after suffering a broken right ankle on the opening drive against Nevada on Oct. 19. He played briefly in a Dec. 1 game against New Mexico on Boise State's first drive, leading the team to a touchdown.