Attorney John B. O'Connor, who helped defend Thomas Junta, told the Boston Herald that the Committee for Public Counsel Services will file the motion Monday in Suffolk Superior Court.
Junta was convicted of involuntary manslaughter in January 2001 for beating Michael Costin on July 5, 2000. Junta was sentenced to six-to-10 years in prison.
Junta testified at his trial that he tried to avoid a fight and only struck Costin in self-defense. A medical examiner said Costin had severe brain injuries, and others said Junta pounded Costin's head and was red-faced with rage.
O'Connor said two issues are at the heart of the appeal: whether Middlesex prosecutors violated a court order requiring them to present all relevant information on medical examiner Stanton C. Kessler before the trial, and whether Kessler made Costin's injuries appear more vicious at trial than he did when discussing them at a professional conference in 2001.
Seth Horowitz, a spokesman for Middlesex District Attorney Martha Coakley, said prosecutors had not received a copy of the motion.
"We are convinced Mr. Junta received a fair trial last year. The courts will review any appeal on the merits," he said.
Kessler could not be reached for comment, the Herald said.