Vinaya non-offence complications? From suttacentral Parajika rules:


  "Non-offenses - There is no offense: if it is unintentional; if he
  does not know; if he is not aiming at death; if he is insane; if he
  is the first offender." PJ 3


What happens to unintentional second offenders? The ignorant/under-informed? If one kills unintentionally, but aware of the offence of killing, where does one stand?
The Patimokkha Rules
Translated &amp; Explained
by Thanissaro Bhikkhu, on pages 49 through 50, uses the word "or" (not "and"):


  Blanket exemptions. In addition to bhikkhus who do not know they are
  being assaulted or do not give their consent when they do know, the Vibhanga
  states that there are four special categories of bhikkhus exempted from a penalty
  under this rule: any bhikkhu who is insane, possessed by spirits, delirious with
  pain, or the first offender(s) (in this case, Ven. Sudinna and the bhikkhu with the
  monkey) whose actions prompted the Buddha to formulate the rule. The
  Commentary defines as insane anyone who “goes about in an unseemly way,
  with deranged perceptions, having cast away all sense of shame and 
  50
  compunction, not knowing whether he has transgressed major or minor training
  rules.” It recognizes this as a medical condition, which it blames on the bile. A
  bhikkhu under the influence of a severe psychosis-inducing drug would
  apparently fall under this exemption, but one under the influence of a more
  common intoxicant would not. As for spirit possession, the Commentary says
  that this can happen either when spirits frighten one or when, by distracting one
  with sensory images, they insert their hands into one’s heart by way of one’s
  mouth (!). Whatever the cause, it notes that insane and possessed bhikkhus are
  exempt from penalties they incur only when their perceptions are deranged
  (“when their mindfulness is entirely forgotten and they don’t know what fire,
  gold, excrement, and sandalwood are”) and not from any they incur during their
  lucid moments. As for a bhikkhu delirious with pain, he is exempt from penalties
  he incurs only during periods when the pain is so great that he does not know
  what he is doing.
  
  These four categories are exempted from penalties under nearly all of the
  rules, although the first offender for each rule is exempted only for the one time
  he acted in such a way as to provoke the Buddha into formulating the rule. I will
  only rarely mention these categories again, and—except where expressly stated
  otherwise—the reader should bear them in mind as exempt in every case.


So I read that as saying that any one of the conditions is reason for it's being a non-offence; and that the only condition for exemption that's only applicable once is being a first offender.

On page 29 it says,


  If any of these factors is missing, the penalty changes. For instance, object: If
  the bhikkhu kills a dog, the penalty is a pacittiya. Perception: If he cremates a
  friend, thinking that the friend is dead, then even if the friend is actually alive but
  severely comatose, the bhikkhu incurs no penalty. Intention: If he accidentally
  drops a rock on a person standing below him, he incurs no penalty even if the
  person dies. Effort: If he sees a person fall into the river but makes no effort to
  save the person, he incurs no penalty even if the person drowns. Result: If he
  tries to kill a person, but only succeeds in injuring him, he incurs a thullaccaya.


Pages 76 though 78 (which I won't quote here in full) discuss intention w.r.t. killing; briefly:


  The non-offense clauses state that there is no offense for a bhikkhu who acts
  unintentionally, not knowing, or without aiming at death. In the Vinita-vatthu,
  unintentionally is used to describe cases in which a bhikkhu acts accidentally, such
  as dropping a poorly held stone, brick, or adze; removing a pestle from a shelf
  and accidentally knocking off another one. Not knowing is used in cases in which
  the bhikkhu deliberately does an action but without knowing that his action
  could cause death. An example would be giving food to a friend not knowing
  that it is poisoned. Not aiming at death is used in cases where the bhikkhu
  deliberately does an action but does not intend that action to result in death.
  Relevant examples include trying to help a bhikkhu who is choking on food by
  slapping him on the back and inadvertently causing his death; telling a bhikkhu
  to stand on a piece of scaffolding while helping with construction work, only to 
  see the scaffolding collapse; describing the joys of heaven to an audience, only to
  have a member of the audience decide to commit suicide in hopes of going there.
  
  Thus, to fulfill the factor of intention here, a bhikkhu must be acting
  intentionally, knowingly, and aiming at death.


Page 78 suggests that acting when aware of danger might or might not count as intentional:


  In discussing the topic of pitfalls, the Commentary also treats the issue of
  how much of an intention counts when setting up a situation that might cause
  death. Specifically, it asks whether—while one is digging a hole for another
  purpose—a passing thought that “this hole could kill anyone who fell into it”
  would fulfil the factor of intention under this rule, or whether this factor would
  be fulfilled only if the original purpose for digging the hole was to cause death.
  The Commentary notes that opinions are divided on this point, but it sides with
  the latter position.