[16][17][18] On 15 December 2023, a 32-year-old father and his two-month-old daughter in a stroller were shot dead in Klánovice Forest on the eastern outskirts of Prague, approximately 25 kilometres (16 mi) away from where the later Charles University attack would take place.

[19] The police conducted a detailed search of the entire forest with hundreds of officers, while a special task force was set up in order to find the perpetrator.

The scope of investigation was first directed at owners of registered firearms matching the ballistic report from the crime scene, which initially limited the search to about 30,000 people.

[27] The chief detective of Prague's 1st General Crime Unit stated because Kozák lived in the Central Bohemian Region, they were a few days short of being able to prevent the University attack.

called medical emergency line,[32] stating that Kozák was planning to take his own life, that "he could be dangerous",[2] that he told her "he will do something she will hear about",[33] and that he was on route from his hometown of Hostouň to Prague.

[29] Prague police dispatcher issued an APB, according to which Kozák was sought due to suicide threats, he may be dangerous and also may be connected to a violent crime, possibly a murder.

[2] Before starting the attack, the perpetrator placed his ID, fourth floor plan with handwritten notes about classrooms capacities, unopened alcohol bottle, and Rivotril pack of medicine under the bathroom window.

[2] At 13:30 CET, two police units, altogether six officers, entered the main building of the Faculty of Arts on Jan Palach Square,[35] where they talked to the reception personnel as well as to two Vice-Deans whom they met in the corridors.

[47][48] Dozens of heavily armed police officers, including Prague SWAT unit, spread out in the crowded area where Christmas markets were taking place.

Several of the students present in other 4th floor classrooms fled through windows towards the terrace, then climbed an exterior ledge on the other side of the building and later jumped to a third-floor balcony, sustaining injuries from the fall.

While avoiding the perpetrator, Hercík entered numerous classrooms and warned the people inside about the ongoing attack, making sure that they lock the doors, switch off lights, and remain quiet.

[1] Between 15:18:54 and 15:18:59, as the perpetrator was again briefly visible to those on the ground, a plain clothes detective positioned at Jan Palach Square fired three shots from his Glock pistol.

On page 39, it was stated that "it cannot be concluded that the police knew that the lives of the students of the Faculty of Philosophy in the building on Jana Palach Square were in real and immediate danger."

Opposition ANO party members were angered by the redaction of the document and stated their intent to establish a Parliamentary Inquiry Commission with full investigative powers in order to receive complete information about the case.

"[36] Interior Minister Vít Rakušan also commented that authorities had no indication of anyone else at risk other than Kozák himself,[34] and that police knew that the father was murdered only after decommissioning the improvised explosive device, which took place after the University attack was over.

[36] According to Lidové noviny, the circumstances of the father's death were clearly pointing to murder, police also had information about Kozák's firearms possession, and Matějček personally ordered a tactical unit to be present in the Staroměstské náměstí area before the attack commenced.

[36] Moreover, on 26 June 2024, online daily Seznam zprávy published action reports filed by the policemen that had unsuccessfully searched for the perpetrator in the School of Arts main building.

University official labeled Matějček's statement as a "lie", claiming that reviewing of previous footage can be done immediately, but the police officers asked for it only hours after the attack.

[67] Interior minister Vít Rakušan called on mayors across the country to cancel New Year's fireworks displays in light of the killings and urged citizens to mark the event peacefully out of respect for those traumatised by the shootings.

[94] The new act, which will become effective in 2026, includes several changes, such as requiring businesses to report suspicious purchases of firearms and ammunition to police, requiring gun owners to undergo a medical examination every five years as opposed to 10 years under the current laws, giving doctors access to databases to find out if their patients are gun owners, and expanding reasons for preliminary seizure of firearms by police.

[97] Investigators concluded that the shooter was a lone assailant, that the attack was not planned to target anyone in particular, and that the motive was that he felt misunderstood by society and wanted to draw attention to himself.

[105] Kozák successfully defended his bachelor's thesis at the Institute of World History, Faculty of Arts, Charles University, entitled The Antagonism Problematics of Galician Peasant Revolt and Kraków Uprising in the Year of 1846.

[107] The perpetrator had no prior criminal record,[51] and had also passed an enhanced background check by the Civil Aviation Authority as part of a hiring process for his job at the Václav Havel International Airport.

[111] A Telegram account attributed to him contained writings in fluent Russian[112] that praised two school shooters from Russia, namely Ilnaz Galyaviev and Alina Afanaskina, and described suicidal tendencies.

"Psychologist expert opinion (post mortem)[30]Czech Police Chief Martin Vondrášek [cs] said that the perpetrator had a gun license and owned eight firearms,[103] which he obtained as part of his plan to commit a mass murder.

[2] According to police ordered post-mortem psychological evaluation, Kozák had personality that was "schizoid with narcissistic and dissociative traits and a very solid IQ", but did not suffer from any particular mental disorder.

[50] From beginning of 2023, Kozák gradually changed his lifestyle in a way aimed at imitation of Keiji Kiriya from All You Need Is Kill Japanese science fiction, which had previously been the topic of an essay he wrote at high school.

[125] President Petr Pavel expressed his "sincere condolences" to the family and friends of the victims via social media, while also cutting short a trip to France.

[126][127] Fiala later announced a day of mourning for 23 December, with flags flying at half-mast and a minute of silence held at noon, along with the ringing of bells for the victims.

[67] In a social media post, SPD MP Jiří Kobza blamed the "inclusive progressive school system" at the Faculty of Arts for creating the shooter.