According to IPN president Dr Karol Nawrocki, chief among the renewed investigations are three opposition priests who died in suspicious circumstances in 1989.
Poland's Police Central Investigation Bureau (CBSP) has seized 48 firearms, 30,000 rounds of ammunition and several grenades in an operation carried out in three provinces.
Determined to track down the person who abandoned them, stable owner Justyna Banaszewska set about rallying support from the local community.
Regional prosecutors in the southern city of Gliwice have launched an investigation into the Zofiowka mine disaster where a tremor and methane discharge killed at least six miners.
The 2010 Polish presidential plane crash in Smolensk, Russia, that killed 96 people including the president, was a result of "an act of unlawful interference", said Antoni Macierewicz, head of a special sub-committee investigating the cause of the air disaster.
Poland is prepared to send representatives to Ukraine to help investigate apparent war crimes committed against civilians by Russian troops in the Ukrainian town of Bucha close to Kyiv, a deputy foreign minister has said.
Polish prosecutors have offered their Ukrainian counterparts help in investigating alleged war crimes committed on civilians by Russian troops in the Ukrainian town of Bucha near Kyiv, Poland's National Prosecution said on Monday.
Poland's media watchdog, the KRRiT, is looking into a broadcast by a Warsaw radio station that may have contained pro-Kremlin propaganda on Russia's war on Ukraine.
Polish prosecutors will hold an investigation into the possibility Russia has committed "the crime of offensive warfare" against Ukraine, Zbigniew Ziobro, the justice minister, has announced.
At a joint press conference, the signatories from opposition parliamentary groups and caucuses declared support for Paweł Kukiz's candidature as head of the commission.