That is something that bugs me. Working at someone's business as a welder you usually wouldn't know the actual address of the CEO. You might learn general area or sub division, but not the actual address.
The security system actually bothers me less. Didn't he enter during the daytime? You have two parents, a child, 2 dogs and a housekeeper going in and out. The door could have been open or he could have accosted any of them as they came or went. As far as what he did to the security system, once he had them under control he could get any info he needed about the system.
Nowdays all you need is a computer with an internet and a name to find out the address.