At 4th level, upon successfully hitting his studied target with a melee attack, an investigator can make a studied strike as a free action against that target to deal additional damage. The additional damage is 1d6 at 4th level and increases by 1d6 for every 2 levels thereafter (to a maximum of 9d6 at 20th level). The damage of studied strike is precision damage and is not multiplied on a critical hit; creatures that are immune to sneak attacks are also immune to studied strike.
If the investigator's attack used a weapon that deals nonlethal damage (such as a sap, a whip, or an unarmed strike), he may choose to have the additional damage from studied strike be nonlethal damage instead of lethal damage. If the investigator chose to have an attack with a lethal weapon instead deal nonlethal damage (with the usual –4 penalty), the studied strike damage may also deal nonlethal damage.
The investigator must be able to see the target well enough to pick out a vital spot and must be able to reach such a spot. An investigator cannot use studied strike against a creature with concealment.