LEO are sworn to apprehend violent criminals. They cannot "stand down" and do their job at the same time....
Let's suppose that the officer did stand down and this thug got away. How would you react if this lucky thug then shot his girlfriend as he had already threatened?
Would you blame his actions on the trauma of his being chased by the cop?
The thug in this case had a gun in his hand and represented a threat to humankind whether he was running away from or toward the officer sworn to shield the general society from such vermin as the subject of this sentence.