A gas cylinder explosion was initially considered to have caused the building to collapse. Five people were killed and 21 injured in the incident in Poznan.
An apartment building in Poznan could have been brought down to cover up a murder, prosecutors in Poland said on Monday.
The building with 18 apartments collapsed early Sunday, leaving five people dead and 21 injured. The explosion of a gas cylinder was considered to be a possible reason.
Polish news agency PAP reported on Monday that investigators were almost 100 percent certain that explosives might have been used to cover up the the murder of a woman.
Magdalena Mazur-Prus, a spokeswoman for the regional prosecutors' office, did not confirm the PAP report. But she did not deny that the building could have faced an "intentional" attack.
Citing anonymous sources, the news outlet wPolityce.pl said that a woman had been decapitated some time before the incident took place.
Mazur-Prus said three women and two men had died in the explosion. Forensics experts were performing post-mortems.
ap/rc (AP, dpa)