In the book
Savage Foes of North America they indicate a sample code of conduct for a NPC Cyber Knight they've provided. This one is based on the European knight traditions, rather than from another culture. Ben's code should represent his background, but he is free to use this one for simplicity. His choice.
[ +- ] Code of Chivalry
CODE OF CHIVALRY
1. To Live
Live one's life so that it is worthy of respect and honor.
Live for freedom, justice, and all that is good.
2. Fair Play
Never atack an unarmed foe.
Never use a Psi-Sword on an opponent notequal to the atack.
Never charge an unhorsed opponent.
Never atack from behind.
Avoid cheating.
Avoid torture.
3. Nobility
Exhibit self-control.
Show respect to authority.
Obey the laws if they do not supersede therights of life.
Administer justice.
Administer mercy.
Protect the innocent.
Respect women.
4. Valor
Exhibit courage in word and deed.
Defend the weak and innocent.
Fight for an ideal, like freedom.
Fight with honor.
Avenge the wronged.
Never abandon a friend, ally, or noble cause.
5. Honor
Always keep one's word of honor.
Always maintain one's principles.
Never betray a confdence or comrade.
Avoid deception.
Respect life.
Honor all life.
Respect all views of life.
6. Courtesy
Exhibit manners.
Be polite and atentive.
Be respectful of host, women, and honor.
7. Loyalty
To one's principles and heart.
To one's friends and those who lay their trust in thee.
To the Code of Chivalry.
With this code, I don't think Ben has violated anything. He did not fail to protect the innocent, as the demon can not be considered to be innocent.
If anything, does a tendency toward mercy extend to criminals subdued by force and executed? I think that would be extreme, unless Ben does the executing himself without fair explanation of his judgement and sentence.