Depends on your philosophy I suppose. For example, Christianity teaches that failing to do good is itself a sin. So that suggests that an omission could be cons

Depends on your philosophy I suppose. For example, Christianity teaches that failing to do good is itself a sin. So that suggests that an omission could be considered to make someone guilty. I suspect that all modern legal systems have the concept of negligence which could result in someone being considered guilty for someone's death. I imagine in that case whether that's "murder" would come down to whether you mean a legal definition (which might call it something else like "manslaughter") or the colloquial definition.