The death toll from Saturday's mass shooting in the Polish city of Krakow has risen to nine, after police found the bodies of three more people — believed to be the gunman's parents and sister — at his home in another town. Poland's National Prosecutor's Office launched a terrorism investigation on Sunday, as officials said the attacker was fascinated by far-right ideology.

The gunman opened fire at random in Krakow's Main Market Square, the UNESCO-listed historic heart of Poland's second city, shortly before 3pm local time on Saturday. Six people were killed in the square — four women and two men, including a British national and three Polish citizens — and at least 15 other people were wounded.

The attacker was a 24-year-old Polish man, named in Polish media as Michal O. He was masked and dressed in military clothing, including a bullet-proof vest, and was carrying a semi-automatic rifle, reported to be an AR-15. Police shot and wounded him at the scene, and he remains in critical condition in hospital.

Two police officers were wounded as they chased the gunman through the square. Police named one of them as Senior Constable Jakub Kulik, saying he confronted the armed attacker without hesitation, and the second as Senior Constable Artur Moriński. One of the officers was in a serious but stable condition. Images shared on social media showed the two officers firing back at the gunman, with one managing to wound him despite his own injuries.

Hours later, police searching the suspect's home in Ostrowiec Swietokrzyski, roughly 150 to 200 kilometres north-east of Krakow, made a second grim discovery. The bodies of two women and a man were found inside the property: the gunman's father, aged 53, his mother, aged 52, and his sister, reported to be 20 or 21. Police said injuries found on the bodies were preliminarily assessed as gunshot wounds, and that seven firearms were seized from the flat. Weapons were also found in the suspect's car.

Prime Minister Donald Tusk said there were strong indications that the three were the gunman's immediate family, describing the discovery as “the next acts of this tragedy”. He had earlier called the shooting in the square an act of “terrorism”, and warned that a significant amount of weaponry may have been inside the house.

Interior Minister Marcin Kierwinski said the gunman was “fascinated by far-right ideologies” and held ultranationalist views. Investigators quoted in Polish media said he had no previous criminal record and was a member of a shooting club along with his father. Poland's Internal Security Agency and Military Counterintelligence Service are assisting the investigation, and police have said the gunman acted alone and that there is no second suspect.

On Sunday morning, the usually busy square was sealed off with red-and-white tape as mourners brought candles and flowers to the scene. Most souvenir shops stayed closed, police checked the bags of workers at cafes and restaurants on the square, and black flags and Polish flags with black ribbons were seen across the city. Warsaw announced two days of national mourning from Sunday, and Krakow's own mourning period runs until Wednesday, 11 November.

Residents spoke of their shock at an attack in a city long regarded as one of Europe's safest. “It's one of the safest places on Earth genuinely... I did not expect anything like this to happen to us,” Weronika Filar, 27, told AFP. “Our city will never be the same.” Part-time city guide Krzysztof Stepien, 28, said: “Nothing like this has ever happened here, and I hope it never will again.” Britain's Prime Minister Andy Burnham said he was “shocked and saddened by the appalling shooting”.

The suspect remains in hospital, and police have not yet said when the three family members died or what charges he will face. Investigators are still establishing the motive and the full sequence of events. The attack is already Poland's deadliest shooting since 1989, and the discovery of the three bodies at the gunman's home has deepened a tragedy that has stunned the country.