US Authoritarianism

"Felony murder" is a different animal. It's kind of like how even though "rape" is generally defined by a lack of consent, there is also "statutory rape", which one can be charged with, even if the sex was consensual.

To summarize how "felony murder" works:

The felony murder rule is a rule that allows a defendant to be charged with first-degree murder for a killing that occurs during a dangerous felony, even if the defendant is not the killer. The felony murder rule applies only to those crimes that are considered “inherently dangerous,” as the rationale underlying the felony murder rule is that certain crimes are so dangerous that society wants to deter individuals from engaging in them altogether. Thus, when a person participates in an inherently dangerous crime, he or she may be held responsible for the fatal consequences of that crime, even if someone else caused the actual death.

In this case, the "inherently dangerous" felony was armed robbery.