In this area, police officers have to assume anyone they stop is carrying drugs. Way too many officers have been shot and/or killed when stopping drug runners. At times it seems that the flags at law enforcement agencies are permanently set at half-staff.
The cartels use illegal aliens to run drugs across the border, so many times an illegal alien stop will produce drugs in distribution quantity. In this country fleeing from peace officers is a felony. For just being illegal aliens, there was no need to run. All immigration will do is hold them for a few days. Where they get 3 hots and a cot, in safe conditions. Then they are sent back south. From what I have been told, most illegal aliens will stop when challenged by officers. So these illegals running sent a different message to officers.
As for these officers,they were within agency policy. It appears they shot the engine. The dead died due to the crash. Since the driver decided to run, the deaths are legally his responsibility. They died directly due to his commission of a felony.