Prosecutor Jeff Ashton described Jessie Baskin, 22, as being "most-consistently identified as the most enthusiastic" band member participating in the hazing ritual that led to Robert Champion's death. Baskin was beating Champion with his hands and feet, Ashton said.
According to the Orlando Sentinel, a co-defendant earlier said in a sworn statement that other musicians had to pull Baskin off Champion.
A deal with prosecutors calls for Baskin to spend nine years in prison, although his attorneys can argue for a lighter punishment when a judge sentences him in February.
Champion collapsed and died in November 2011 after prosecutors said he walked down the aisle of a bus as other band members beat him with fists and instruments. The bus was parked outside an Orlando hotel following a football game.
Also Wednesday, Harold Finley, 21, pleaded guilty to felony hazing. In exchange for his plea, prosecutors dropped manslaughter and misdemeanor hazing charges and he was sentenced to one-year of house arrest, four years of probation, 100 hours of community service and he must complete an anti-hazing course.
Judge Marc Lubet said the sentence would also be contingent on Finley graduating from a college he is enrolled in and continuing to cooperate with prosecutors.
"I want you to graduate from college and go and make something of yourself," Lubet told Finley.
Ashton told the judge Finley participated in the hazing of another band member the night Champion died, but he was only present for Champion's hazing and did not hit him.
Six remaining defendants also had their cases set for trial, but they will continue to discuss possible plea agreements.
Champion's mother, Pam Champion, listened to Finley's sentencing by phone. As she had done during previous sentencing hearings, she talked about what her family has been through.
"There is a time when you must really answer for what you have done," she said, speaking to Finley. "When that time comes, there will be no lawyers ... It will just be you."
Fifteen former band members were charged with manslaughter and hazing in Champion's death.
Eight now have accepted deals, with seven already sentenced to combinations of probation and community service.
Another defendant, Caleb Jackson, pleaded no contest to manslaughter in April, but has yet to be sentenced.
Champion's death led to the departure of the band's longtime director, the abrupt resignation of the FAMU president James Ammons and the suspension last year of the famed marching band. The school has since made sweeping changes to end a culture of hazing. The famed Marching 100 band returned to the field Sept. 1.
For Baskin's sentencing, Aston said he will keep an open mind.
"I want to listen to what they're presenting. But our position was he should do the nine years, which is the minimum guideline sentence," he said. "I don't know what statutory mitigating circumstances they're going to argue for downward departure. None immediately jump to mind."