Worcester District Attorney Joseph Early Jr. says Westborough police responded to an apartment complex in town at about noon on Friday for a domestic violence dispute.
Early says the attack was still taking place when officers arrived and one opened fire, killing one of the people involved.
Both the person who was shot and the victim were taken to the hospital.
The police officer was also taken to the hospital as a precaution.
No names have been released and the case remains under investigation.
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