1) Il y avait une femme que j’ai vue tuer.
2) Il y avait une femme que j’ai vu tuer.
Both of these sentences are very similar but have completely different meanings. The verb voir means to see and is is conjugated in the pass tense above and is written both as vu and vue, which translates as “saw”. The verb voir is also considered a verb of perception, meaning that it is a verb that refers to one of the five senses (touch, taste, sight, sound and smell).
The rule is that a verb of perception (voir, or in this case vu) can be altered by the gender of the object ( in this case it’s “une femme” [a lady] which is a feminine noun) if the object (une femme) is both the one being perceived and also the actor (the doer, if you please) of the infinitive verb. The infinitive verb (a verb that has not been conjugated) is represented by tuer, which is the verb “to kill”.
Case 1: If la femme is both perceived, here meaning that she was seen, and she is also the actor of the infinitive verb tuer (to kill), the verb of perception is altered to show gender agreement. The result is vu becomes vue.
Case 2: If she is only perceived by one of the five senses but is not the actor of the infinitive verb tuer, the verb of perception, vu, is unaffected and remains written as vu.
Sentence #1 can be translated as “There was a woman who I saw kill.” (As in, the woman is the killer)
Sentence #2 however translates to mean “There was a woman who I saw killed.” (As in, the woman is the victim.)
Now those are two sentences with opposing meanings with significant difference in meaning. And all of that is due to that seemingly minor addition of the letter e !