My take. The officer did overreact. It was right to fire him. But the man was lying and his story did not track. No one would use a shovel to see if a dog was in a garage. Also he changed his story about living there. First he said he did live there but then changed it to he was “in and out” when asked about having a key.
My gut instinct is that he did want to get into his mom’s house by breaking in but when he could not pry the garage door he figured he would just wait for her. He probably wanted some money from her. I wonder if he has a record of drug charges or B&E.
There are rumors she had a restraining order against him, which would explain a lot. Perhaps some resourceful FReeper could determine the veracity of that allegation.