The key to both the legal standards — defense of life and fleeing a violent felony — is that it doesn’t matter whether there is an actual threat when force is used. Instead, what matters is the officer’s “objectively reasonable” belief that there is a threat.

,,,Officers couldn’t justify their conduct just based on whether their intentions were good. They had to demonstrate that their actions were “objectively reasonable,” given the circumstances and compared with what other police officers might do.

And what’s “objectively reasonable” changes as the circumstances change.

Police can use deadly force if they merely perceive a threat – Vox

This.