Your cited authority doesn't seem to support your position.

The rule holds that, while a landowner must exercise reasonable care to maintain his property so as to prevent injury to a fireman arising from a cause independent of the fire, he is not liable for his negligence in causing the fire. (Emphasis added.) [Citations.] Our cases since have refined the doctrine to protect firefighters only against the risk of injury arising from a cause independent or unrelated to the fire itself. [Citations.] Derived from the theory of assumption of the risk, the fireman’s rule limits homeowner liability based upon the fact that, as a part of their job, firefighters knowingly and voluntarily expose themselves to certain hazards, and that they are specially trained to anticipate and guard against risks ordinarily associated with fighting a fire. [Citations.] Accordingly, although a firefighter may be able to recover for unexpected or hidden dangers that are independent of the fire and attributable to the homeowner’s negligence, he is barred from recovery for injuries caused by obvious dangers which, based on his training and experience, he would reasonably be expected to anticipate and protect against. [Citations.] Further, this is so even if those injuries did not directly result from the fire itself.

As I read it, the exception applies to insulate property owners from liability based on "his negligence in causing the fire." But LeGrier's alleged actions were not negligent, but an intentional tort -- he (allegedly) attacked the police officer with a deadly weapon. This is more like an arsonist intentionally torching a fire station.

I honestly don't think it makes any sense for "assumption of the risk" to extend to the situations where someone is trying to attack or kill the police officer or firefighter in question. I don't think that is properly considered an "ordinary risk" of law enforcement. And I think if someone tries to commit a serious crime, like attempted murder, then I don't see why the law would insulate that person from civil liability arising from the damages he or she has caused.