Dr. Howard Oliver, a former deputy medical examiner in Los Angeles, told CNN Robert Champion's muscles were damaged enough to leak myoglobin -- a protein in muscle tissue that is present in the bloodstream after it is released due to muscle injury. Oliver said the leakage causes kidney failure and death.
"His muscles were beaten so badly that they were destroyed like you would see in a heart attack," Oliver said.
Champion died Nov. 19 while the Marching 100 band was in Orlando, Fla., for a football game. Florida A&M is in Tallahassee.
Last week, the medical examiner declared the death a homicide.
Band members who did not want their names used have told CNN Champion was subjected to an ordeal known as "crossing Bus C," in which victims are ordered to walk from the front of the bus to the back while they are struck repeatedly.
Three members of the band face criminal charges for an alleged hazing incident shortly before Champion's death. In that case, the victim survived.