The original article has very little more information:
http://www.syracuse.com/news/index.ssf/2012/07/rochester_man_shoots_and_kills.html
But I agree that something doesn't seem right.
Did he come through a window? Did they leave the door open?
Either one would make it reasonable to assume that someone in the room was an intruder.
But if he had a key or card, dad got some 'splainin to do.
And why was he carrying his work tool while off duty? If he's not at work, or on his way to/from in uniform, he should have his own personal defensive device.
If it's found that this was not an accident, I hope that gun is treated just like any regular citizens' property used in a crime - melted down.