user-1: If every bad event is because of karma, how can anyone ever murder an arhat?

Killing an Arhat (enlightened being)

is one of the ānantarika-kamma actions.

user43: If I remember correctly, Buddha once said that Devadatta's throwing a rock and hurting Buddha's foot was caused by Buddha's past bad karma from a previous life.
Even for Buddha's and non-returners/Arhats past karma keeps getting resolved until parinibbana.

user-1: 
If every bad event is because of karma, how can anyone ever murder an arhat or buddha?

Question premise might reveal an internal inconsistency - every bad event is not only caused by Kamma.
The Buddha taught that there are 5 natural laws (Niyamas), that causes physical and mental events to take place;

1.    The seasonal laws (Utu-Niyama) related to temperature, seasons and other physical events
2. The biological laws (Bija-Niyama) related to seeds and physical organic order
3. The physical law (Citta-Niyama) related to the processes of consciousness, or to the nature of consciousness which recognises objects etc.
4. The Kammic law (Kamma-Niyama) related to the law of Kamma, (good deeds and bad deeds and their results) 
5. The Natural laws (Dhamma-Niyama) related to certain events: the general law of cause and effect, causality conditionally and unconditionally 
  Trying to further interpretate it will just carry over into  imagination. Only a fully enlightened Buddha can know the intricate workings of kamma.


-1: <p>If every bad event is because of karma, how can anyone ever murder an arhat?</p>

<blockquote>
  <p>Killing an Arhat (enlightened being)</p>
</blockquote>

<p>is one of the <a href="https://en.wikipedia.org/wiki/Anantarika-karma" rel="nofollow noreferrer">ānantarika-kamma</a> actions.</p>
 43: <p>If I remember correctly, Buddha once said that Devadatta's throwing a rock and hurting Buddha's foot was caused by Buddha's past bad karma from a previous life.</p>

<p>Even for Buddha's and non-returners/Arhats past karma keeps getting resolved until parinibbana.</p>
 -1: <blockquote>
  <p>If every bad event is because of karma, how can anyone ever murder an arhat or buddha?</p>
</blockquote>

<p>Question premise might reveal an internal inconsistency - every bad event is not <em>only</em> caused by Kamma.</p>

<p>The Buddha taught that there are <a href="http://www.purifymind.com/BuddhismKarma.htm" rel="nofollow noreferrer"><em>5 natural laws (Niyamas)</em></a>, that causes physical and mental events to take place;</p>

<blockquote>
  <p><em>1.    The seasonal laws (Utu-Niyama) related to temperature, seasons and other physical events</em></p>
  
  <p><em>2. The biological laws (Bija-Niyama) related to seeds and physical organic order</em></p>
  
  <p><em>3. The physical law (Citta-Niyama) related to the processes of consciousness, or to the nature of consciousness which recognises objects etc.</em></p>
  
  <p><em>4. The Kammic law (Kamma-Niyama) related to the law of Kamma, (good deeds and bad deeds and their results)</em> </p>
  
  <p><em>5. The Natural laws (Dhamma-Niyama) related to certain events: the general law of cause and effect, causality conditionally and unconditionally 
  Trying to further interpretate it will just carry over into  imagination. Only a fully enlightened Buddha can know the intricate workings of kamma.</em></p>
</blockquote>
