Nouns from Participles
In Polish, participles (verbs functioning as adjectives) can often be used as nouns. This is called substantivization. Instead of modifying a noun (e.g., "the accused man"), the participle stands entirely on its own ("the accused").
Because they originally act as adjectives, these nouns decline exactly like adjectives. This grammar structure is extremely common in formal, journalistic, and legal contexts to describe people by their current role, state, or what has been done to them.
Passive Participles: The Receiver
Many of these nouns are derived from passive participles, which typically end in -ny or -ty. They describe a person who has received an action. For example, oskarżyć means "to accuse," so the passive participle oskarżony acts as the noun for "the accused."
You will see many similar terms in criminal justice and police work to describe individuals caught up in a case, such as poszkodowany or pokrzywdzony (the injured party/victim) and zatrzymany (the detainee).
Active Participles: The Doer
While passive participles describe what happens to someone, active participles describe what someone does. These end in -ący and describe a person actively carrying out a function or role.
For instance, the verb przewodniczyć (to preside) becomes przewodniczący, meaning "the chairman" or "presiding judge." Similarly, prowadzić (to lead/host) gives us prowadzący (the host).
More States and Courtroom Roles
This pattern applies to a wide variety of legal statuses. Notice that zmarły (the deceased) comes from a past participle, but it functions in the exact same way, declining like a standard adjective.
As a trial unfolds, a person's status may change, or they may be contrasted with someone else. Note how the following examples place different substantivized participles side by side. An arrested person (aresztowany) is contrasted with someone still wanted (poszukiwany), while the accused (oskarżony) faces the one bringing the complaint, the complainant (skarżący).