They fired at the first stop because the kill zone had been meticulously prepared. They were not going to allow Lavoy to surrender at the first stop. He was being herded to the kill point.
For perspective only, from the Portland, Oregon Police Directives Manual.
First please note this:
Members should be aware the Bureau’s force policy is more restrictive than the constitutional standard and state law.
http://www.portlandoregon.gov/police/article/526353
Then with that in mind:
0630.05 Vehicle Pursuits http://www.portlandoregon.gov/police/article/526054
Pursuits in General
The decision to pursue must be based on the belief that the benefit of capture exceeds the risk that the pursuit creates. This Risk / Benefit analysis must be constantly reassessed during the pursuit. The circumstances justifying the decision to pursue must exist at the time of initiation. The decision to continue in or terminate a pursuit may include additional information developed during the pursuit. Suspect’s driving behavior, which did not exist prior to the pursuit, should not be used to justify continuing the pursuit.
Prohibited Pursuits
a. Persons whose identities are known, who can be apprehended at a future time, and whose driving or conduct does not create an imminent threat of serious physical injury or death, will not be the subject of a pursuit. The sole exception to this prohibition is if the reason for the pursuit was his/ her involvement in a life-threatening felony.
Pursuit Intervention Strategies
d. Barricading: Barricading is considered deadly physical force and subject to DIR 1010.10. (ed. 1010.10 Post Deadly Force Procedures http://www.portlandoregon.gov/police/article/526379 )
1. Barricading requires the approval of a supervisor. Furthermore, the barricade must be set up in such a manner as to afford the fleeing suspect ample time to see the barricade and stop his/her vehicle.