The shooter from Krakow died in hospital.
The Little Poland County Police Department said the man died in the early morning hours of Nov. 9.
After being injured during his arrest, he remained in critical condition.
The shooting incident took place on November 7 in the center of Krakow: six people were killed, and at least 16 others were injured.
Earlier it was reported that the police are also investigating the murder of three of his family members.