Detentions and reprisals against participants of the events started already in the evening of June 28th 1956. According to figures of the Security Office, by August 8th 746 persons were subject to apprehension or mass detention. The arrested were mainly transferred to the "filtering point" established in the garrison rooms in the vicinity of the Poznań airport of Ławica, where persons apprehended in the streets or at home were treated brutally. The arrested were transferred from the "filtering point" to prisons in Poznań and in the region. Following initial interrogations, more than half of all persons were set free, and the rest was either detained or arrested on various charges. The great majority of those detained (almost 80%) were workers.
The main theme of the investigation into the Poznań events was not so much finding out the course of events, their participants or the scope of crimes committed, but proving the following thesis put forward by communist authorities: June events have been a provocation prepared and carried out by American and West German secret services and reactionary underground, and the riots against the people's state have been pre-planned and supervised.
Those detained and arrested received various treatment. Many cases of insulting, beating, battering or torturing have been reported. Some of the accused had been so badly injured during the investigation, that the prosecutors either released them from prison or assigned for trials scheduled for later time in order to avoid showing them in court.
The investigation into the events focused on the theme of provocation, the strike and demonstration leadership and controlling the fights with the army and Security officers. However, the investigation results failed to prove any imperialist provocation or a provocation carried out by anticommunist underground; no pre-planned and organised nature of the events was found either. A similar conclusion - no traces of any connections between the initiators and organisers of barricade construction, setting fires or taking firing positions - was drawn in respect of the third theme. All findings of the investigation have revealed the spontaneous and impulsive nature of the events and general population support for the riots.