Scenario 1: Justin stabs Jason with a knife, causing an injury that is serious, but very rarely results in death when quality treatment is received. Jason arrives at the hospital, but due to negligence or incompetence on the part of the doctor he dies.
He would be legally liable for this. I would say he is also morally responsible as well
Scenario 2: Justin stabs Jason with a knife, causing an injury that is serious, and very often results in death, regardless of how quickly the injury can be treated. Nonetheless, because of a combination of factors the doctors are able to save Jason from dying. However, Jason dies less than a month later from an infection associated with the knife wound and it's treatment.
He would be legally liable for this. I would say he is also morally responsible for this too
Scenario 3: Justin stabs Jason with a knife in the heart, causing a serious injury that usually results in death. The doctors are nonetheless able to treat the injury and Jason seems to be on the road to recovery. Three weeks later Jason is at home reading Heidegger and trips over something, falling into his coffee table and hitting his chest. He dies before anyone knew what had happened. The coroner determines that if he had been healthy he would most likely have been fine, but because of his weakened state and recent trauma, the impact with the coffee table was too much for him to handle.
He LIKELY would not be legally liable for this death as there is an intervening occurrence. I would still say he is morally liable.
Is Justin morally or legally responsible (two separate issues) for Jason dying in any of these three scenarios, and if so, why, and to what extent? Also, if he is legally responsible, what should he be charged with?
There is not enough info to determine what he should be charged with as much would depend on intent and the reason he was stabbing him.