In Minnesota he could have taken steps to using deadly force...
At least three conditions must concur to excuse or justify homicide under SSSS 609.06 and 609.065:
(1) The killing must have been done in the belief that it was necessary to avert death or grievous bodily harm.
(2) The judgment of the defendant as to the gravity of the peril to which he was exposed must have been reasonable under the circumstances.
(3) The defendant's election to kill must have been such as a reasonable man would have made in light of the danger to be apprehended.
Personally I feel he was justified to shoot them before they messed with his daughter.