Wrongful death is a statutory claim. Created by state law, not common law. That allows certain family members to sue when a loved one is killed by another's negligence, recklessness, or intentional act. The claim is separate from any criminal prosecution arising out of the same death.
Missouri's wrongful death statute (§ 537.080) gives priority to spouse and children, then parents, then siblings. Illinois's statute (740 ILCS 180/2) gives the claim to the estate on behalf of next of kin. Damages can include medical and funeral expenses, lost income the deceased would have provided, and loss of companionship.
Both states also recognize 'survival actions' for the deceased's pre-death pain and suffering, which is a separate claim.