The trial was a bench trial, which means it was decided by a judge, not a jury. Judge Richard Welch heard the case.
Prosecutors say Steve Amos, 34, assaulted the baby multiple times and his girlfriend at the time -- Heather Dragotta, 33, the child's mother -- allowed the abuse to happen when the couple lived together in North Andover in 2010.
Amos was convicted of three counts of assault and battery on a child with injury and three counts of permitting injury to a child, District Attorney Jonathan Blodgett's office confirmed. Dragotta was convicted of one count of permitting injury to a child.
Sentencing is scheduled for Nov. 5.
In June 2010, the baby was rushed to Lawrence General Hospital with a brain hemorrhage -- determined to be the result of shaking the baby violently -- as well as almost two dozen fractures.
Dragotta has insisted that the injuries were the result of vitamin deficiencies and not abuse.