rules of thumb: assassination for assassins

the ad&d dmg has a assassination table for assassins which basically amounts to:

[DC11]  roll (d20 + your level - their level) to assassinate a character

i think this is an abstraction of an offscreen assassination mission, and represents several days of planning and execution, it's not usually what you'd use to determine assassinations played out in person. But you might use it to determine the success of tactics like 'put poison in the guy's wine and then wait'. If it fails, the assassination attempt is discovered.