Learn Polish: Dlaczego oskarżony nie patrzy w oczy ofiary? - Why doesn't the accused look into the victim's eyes?

It is a passive participle acting as a noun (a substantivized participle), translating to the accused or the defendant. Even though it functions as a noun here, it declines exactly like an adjective. For example, if you wanted to say 'I see the accused', it would take the accusative masculine personal form oskarżonego.

If the verb patrzeć is negated (nie patrzy), why doesn't the object change to the genitive case?

The genitive of negation rule only applies to direct objects that would normally be in the accusative case without a preposition. Because oczy is part of a prepositional phrase (w oczy), the preposition w dictates the case. Prepositions always keep their required case regardless of whether the main verb is negated.

Why does w take the accusative case (w oczy) here instead of the locative?

When paired with a verb of motion or directed action like patrzeć (to look), the preposition w takes the accusative to show the target or direction of your gaze. If you used the locative (w oczach), it would mean something is physically located inside the eyes, such as tears or dust.

What is the base form of ofiary, and does it only mean victim?

The base form is the feminine noun ofiara. Here it is in the genitive case to show possession (eyes of the victim). While it means victim or casualty in a legal or medical context, it also translates to sacrifice or offering. In everyday slang, it is frequently used to describe a clumsy or helpless person, similar to klutz or loser.