Running to get a gun to use against an assailant/tresspasser doesn’t seem like planning prior to commission.
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OK. How about the situation as it actually happened? Running to get a gun to use against the boy you know your daughter invited into the house when you were gone, when you knew before you got there that the boy was in your house by your daughter’s own invitation does or does not sound like premeditation.
Try to remember that he was alerted to the situation ahead of time. From the linked story: “He said a friend called that morning to say Guzman’s car was parked down the road.”
Premeditation would be going to the room armed intending to kill Guzman. Not running to get a gun after a possible alleged assault and subequent barricade.