Short for Neminem captivabimus nisi iure victum, (Latin, "We shall not arrest anyone without a court verdict").
In Poland and Polish-Lithuanian Commonwealth it was one of the basic rights, stating that the king can neither punish nor imprison any member of the szlachta without a viable court verdict. Its purpose is to release someone who has been arrested unlawfully. Neminem captivabimus has nothing to do with whether the prisoner is guilty, only with whether due process has been observed.
It was introduced by king Wladyslaw Jagiello in the acts of Jedlnia (1430) and Cracow (1433) and remained in use until the Partitions of Poland. The same acts guaranteed, that he shall not confiscate any szlachta property without a court verdict.
The Four-Year Sejm (1791) decided that the privilege be granted to bourgeoisie and inhabitants of cities.
See also: