WARSAW, Poland (AP) – Prosecutors in Poland’s capital questioned witnesses and gathered evidence Tuesday after a 31-year-old man allegedly placed powerful explosives in a busy downtown area of Warsaw.

Investigators were awaiting an expert’s opinion on the type and potential range of the explosive device that the man allegedly placed on the pavement a few blocks from the presidential palace, according to Aleksandra Skrzyniarz, a spokesperson for the prosecutors’ office in central Warsaw.

Over 300 people were participating in a commemorative march for Polish victims massacred during World War II when police detained the man and evacuated the area Monday. A police bomb squad removed the device, which was inside a backpack.

The suspect has a police record and is to be questioned Wednesday, Skrzyniarz told The Associated Press.

He could face up to eight years in prison on charges of endangering the lives and health of many people with a potential explosion.

Police initially described the situation as “serious” but there was no explosion and there were no reports of anyone being hurt.