CAMBRIDGE, Mass. (AP) — A man convicted of beating another man to death at their sons' hockey practice is asking for a new trial.

An attorney for Thomas Junta claimed on Thursday that the prosecution kept information from the defense that could have been used to undermine the testimony of a key witness.

Junta was convicted of involuntary manslaughter for beating Michael Costin in 2000. He was sentenced last year to six to 10 years in prison.

During the trial, medical examiner Stanton Kessler testified that "substantial force" caused Costin's death. But Junta's lawyers said that at a conference the previous year, Kessler reportedly said fatal injuries like the one that killed Costin could be caused by something as minor as manipulation by a chiropractor.

Prosecutors argued Thursday that Kessler's presentation did not rule out the fact that the injury could also have been caused by major trauma.

The Superior Court judge did not indicate when he would rule on Junta's request. Kessler said he stood by his testimony.