A boy who was 7 when he watched his mother being gunned down along with a friend in Maine testified at his father’s trial Monday. The third-grader told jurors Monday that his father — Joel Hayden, 32, of New Bedford, Mass. — was inside his mother’s house in New Gloucester, Maine, when he saw one of the victims, Trevor Mills, 28, fall through a glass door. He said Hayden then came outside and shot his mother. Hayden allegedly thought his estranged girlfriend, Renee Sandora, 27, of New Gloucester, was having an affair with Mills.