Well, they had a half hour to get 'set up' in the parking lot. They had plenty of armed firepower.
They should have had him put his hands above his head, then handcuffed him. They could have tackled him, and handcuffed him. Where does 'underestimate' include shoot first, then see if he's really armed later?
The gun was in a zippered pouch. Did Mr. Scott point the zippered pouch at the officer? How can you fire a gun that is in a zippered pouch?
They, apparently, wanted to have him put his hands above his head so as to apprehend. Instead, his hand went to his sidearm, and he got himself killed.
He was really armed.
SnakeDoc