According my coworker, once somebody has entered your fenced back yard, it's a home invasion (I believe the Kearns home in question was fenced). He said anything such as a fence, barn, deck, etc. are considered extensions of the home. If you tresspass onto one of these areas, legally it can be considered a home invasion.
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He said from the eyes of law enforcement (at least Weber County's take on it) is that the homeowner acted 100% within the realm of law. He said if this was their case, not only would they not seek to prosicute the home owner, he should be given a pat on the back for how he acted under duress.