Your title is confusing. The actual title from the article is much clearer.

Not really seeing how shooting someone who is fleeing from you is manslaughter, personally.

I'm hoping you're implying he should be charged with murder. This might be one of those cases where it is much more likely a jury would find him guilty of manslaughter rather than murder.

So, I looked up Mass's criminal code, and I think I found why they're doing this. They have a separate section for voluntary manslaughter without a murder charge, and it doesn't seem to require them to show the defendant intended to murder, only that they intended to cause the injury. Which like I think he very clearly did intend to murder, but a regular person might get tripped up on that.

Cop's actions fit the colloquial definition of murder, but maybe the laws are strange in MA.

Either way, the cop's life should be over.

When a cop lies on their official report (and then their own body camera outs their lie - "inconsistent with body-worn camera footage") they should be overcharged (like DA's do to regular people all the time) and prosecuted harder than a non-cop since they are, supposedly, "Paragons of truth and Justice" (says no one I've ever known or respected).

Murder is strict intent and thus harder to prove. Manslaughter isn't, you just have to take steps any reasonable person would understand could lead to death or serious bodily injury.