Polish police have detained nine men for allegedly publicly praising a deadly attack in Krakow online or threatening to copy it. The arrests followed an online crackdown after the attack in Krakow, with investigations linked to posts spreading across social media including Facebook and YouTube, as well as activity on darknet environments. Police said the nine suspects, aged 15 to 38, came from different regions of Poland, including West Pomeranian, Holy Cross, Podlaskie, Lublin, Silesian and Lesser Poland voivodeships. Some posts allegedly celebrated the attacker, while others expressed an intention to carry out a similar attack. Investigators also found references to terrorist Anders Breivik and praise for past terrorist acts in the online content. The Central Bureau of Combating Cybercrime reported that five of the detainees had been linked to troubling online publishing. Police said evidence gathered in the case is strong enough that the detainees are likely to face criminal charges, though prosecutors will decide the legal qualification and any charges. Some of those detained have already been questioned and admitted to their actions. Police said some suspects tried to explain their behaviour by claiming they were under the influence of alcohol. In one case, police carried out searches at the home and workplace of a detainee, including a search of a workplace desk. Investigators are assessing the seized material to understand motivations and check whether the suspects have links to other extremist groups. Police said online monitoring has been ongoing for a long time, but was intensified after the Krakow tragedy to identify potential copycat offenders. Authorities also said they work with major technology companies to speed up the removal of dangerous content. At the latest stage described, the suspects are detained and prosecutors are deciding on the legal qualifications and charges.