Lightning breath is always a lethal attack.
However, a lethal attack is not always used with the intent of committing murder.
If a person combines lethal attacks with nonlethal ones- on a character known to be of high level, then a case can be made that the lethal attacks were still part of a "take them alive" attempt.
However- beginning a routine with a lethal attack- is more suggestive of lethal intent.
Enor's first attack on Elan was a club attack- melee, so could have been nonlethal.
Enor's first attack on Roy (not a bounty, but a stranger) was supernatural lightning breath- known to be lethal.