A former Hawaii Marine and his girlfriend accused of letting their 14-month-old son die after his skull was fractured have been released on $25,000 bail. 

Assistant U.S. Attorney Michael Song says David Lonergan and Tracy Mattos pleaded not guilty on Monday to involuntary manslaughter in the death of Zayden Lonergan. 

Song says their trial has been set for Jan. 15. 

The indictment alleges the couple didn’t immediately get medical treatment for the child in February 2011. The infant was rushed to a Hawaii base fire station and remained unconscious until he died.

The Honolulu medical examiner’s office ruled the death a homicide, with the cause of death “complications of cranial cerebral injuries due to abusive head trauma.”