APD spokesman Officer Simon Drobik told reporters the hero, a 12-year veteran of the National Guard, took action when he saw the pair being attacked Sunday night.
According to police, the incident unfolded Sunday night after the woman's estranged husband crashed his car into their vehicle, got out and fired into their car, which struck the daughter. He then pulled his wife from the car and started beating her.
But then the good Samaritan sprang to action, drawing the attention of the husband, who turned his gun on the Samaritan. That's when the armed citizen opened fire, killing the man.
"She said, 'He saved our lives,'" Drobik said. "I mean, that's how much she was in fear of getting killed by this guy."
The Samaritan is not facing charges. The district attorney is reviewing the case.