The article, taking the advantage of source foundation in the form of public prosecutor’s records, presents a case of crime committed on the AK underground member Józef Sierosławski and his father-in-law Paweł Karczyński as well as brings closer some facts from activity of Grudziądz AK underground network. The murder was committed at night on 10th March 1945 at the police station nr 4 of MO - Civic Police of Grudziądz, located then at 13, Szewska Street. The victims were: Józef Sierosławski, Commander of Grudziądz Inspectorate of Pomeranian AK District, and his father-in-law Paweł Karczyński. The current findings show that the murder inspirers were: Robert Burczyk, Alfons Lackowski, Edward Wawrzynkowski, Włodzimierz Urbański, Edward Wawrzynkowski, Włodzimierz Urbański, AK soldiers who at that time were already the MO officers in Grudziądz. As the crime motive the investigation determined the war time accounts caused by an alleged betrayal of the underground organisation by Józef Sierosławski and supporting him Paweł Karczyński. The conflict cause resided in the arrest wave among the Pomeranian AK soldiers which began on 31 March 1944. In Grudziądz, Gestapo arrested then the Commander of Grudziądz AK Inspectorate, Józef Sierosławski and the underground organisation members including the accused: Robert Burczyk, Włodzimierz Urbański, Edward Wawrzynkowski, Alfons Lackowski. The fact of J. Sierosławski being released the following day after having been arrested by Gestapo, intensified the conviction of his betrayal. During May’s wave of arrests, Józef Sierosławski was detained again, together with his father-in-law, Paweł Karczyński. Almost all the imprisoned were transported to Łódź, in order to hold a further inquiry. It is probable that already then the fellow prisoners might have thought about liquidating Sierosławski, allegedly on organisation’s initiative. Having escaped from the transport during the evacuation of the prisoners in January 1945, the accused and J. Sierosławski and P. Karczyński came back to Grudziądz in early March. Burczyk, Urbański, Wawrzynkowski and Lackowski entered the emerging Civic Police. On 10 March 1945 at the police station nr 4 Sierosławski and Karczyński were stopped and imprisoned in the building’s basement. Soon, at the institution in Szewska Street, there gathered all the accused in the crime case, who decided about a physical liquidation of the two imprisoned men. The direct command of murder was issued by Robert Burczyk to Bronisław Brzuszkiewicz, a policeman in charge of the kitchen at the MO police station nr 4. Although it has not been clarified to the very end, he may have been the one to carry out both executions. The corps wrapped up in blankets were taken out of the police station and buried in the vicinity of Szkolna Street. Thanks to a coincidence a few years later, Jan Zakrzewski, a policeman who was present at the corps burial, passed the information onto the widows. As the result of an undertaken investigation and after a process, on 18 May 1949, convicted of the offence of the murders instigation, Robert Burczyk, Włodzimierz Urbański, Alfons Lackowski, Edward Wawrzynkowski and Tadeusz Damica were sentenced by the District Court in Grudziądz for 6 to 1 year of imprisonment. Bronisław Brzuszkiewicz was found guilty of the two executions and the Court sentenced him for 4 years of imprisonment. Pursuant to successive amnesties, the punishments were meaningly mitigated, including additionally towards pre-trial detention. Second important issue which one can draw from prosecutor’s records is the issue of AK’s activity in Grudziądz. In the city there was one of the Inspectorate of Pomeranian AK District – Grudziądz Inspectorate (“Workshop”, “Hydrogen”), inclusive of Wąbrzeźno and Chełmno, which were in its reach. Since 1943 Józef Sierosławski occupied the position of the Commander of Grudziądz Inspectorate. The most important persons in the organisation were also Robert Burczyk “Kaszuba” – head of intelligence service and information, Edward Wawrzynkowski “Wacław” – commander of Grudziądz district and the trial witness Stefan Kisiel. Organisationally, the city territory was divided in districts administered by district constable. The defendant’s Włodzimierz Urbański’s evidence give grounds to conclude that he held an office of a messenger in garrison’s administration and his duties were connected with an army’s intelligence and in particular with an observation of an armies dislocation. Stefan Kisiel was appointed to be a liaison officer with the District’s administration. The Grudziądz AK network carried out first of all criminal investigation tasks. This activity’s field becomes visible mostly in the evidence of the people connected with the network. The fact which deserves underlining is that a lot of those activities were focused in Grudziądz Junker und Ruh plants (before the war Herzfeld Victorius, popularly called HV), therefore in the place where the Germans located production of parts for bullets V1. The intelligence information from that factory flew directly to Sierosławski, and afterwards to the management of the District’s intelligence. The reports on the subject of that weapon were highly appreciated. It was garrison’s surveillance and occupation of authority’s apparatus, in particular Grudziądz Gestapo that, among other tasks, was emphasised in relations. Walter Ziesener was to be the agent pointed out in the evidence, won over to collaborate, fulfilling a translator’s role in Gestapo head office. Stanisław Kamiński, working in the intelligence structure, remembers him and another Pole – Zawacki, working in the local Gestapo office. The issues revealed alongside the Józef Sierosławski and Paweł Karczyński assassination trial solely indicate some of the Grudziądz AK activity threads. It proves that in the archive source stock there appears a good deal of reserves which might broaden the knowledge about the Pomeranian conspiracy.