Czech police say they are dealing with a spate of copycat shooting threats after a lone gunman killed 14 people at a university in Prague.
Seven people were investigated on Christmas Day alone for making dangerous threats – typically declaring "now it's my turn", according to police – or glorifying the Prague shooting.
Police said on Thursday they are tracking more than 60 social media posts in which people claim they support or want to emulate the gunman, who also injured two Emiratis in the December 21 attack.
Separately, Czech media reports on Thursday said police had found a letter from the gunman confessing to the killing of a father and daughter days before the mass shooting.
Police had linked the two events based on ballistic evidence from Charles University, where the man killed himself after being cornered by police.
Thirteen people were killed in the gunfire and another later died in hospital. The two injured Emiratis have had surgery for their injuries and received a call from Sheikh Hamdan bin Mohammed, Crown Prince of Dubai.
Czech police are themselves being investigated by an inspectorate for their handling of Thursday's events, although Interior Minister Vit Rakusan has defended their response.
The shooter, widely identified as David Kozak, 24, was not known to police and had no apparent links to international terrorism or extreme ideology.
While his motive is not clear, it has emerged that he had a licence for eight weapons, including two long guns, raising questions about the Czech Republic's relatively liberal gun laws.
Investigators meanwhile "have their hands full" as they chase down and arrest the authors of online posts linked to the shooting, according to police in the South Moravia region.
One suspect allegedly posted online about planning a shooting in an entertainment district in Brno, the Czech Republic's second city.
Although no weapon was found and the person said the threat was a hoax, the poster could be prosecuted for "spreading alarmist news". A second suspect who posted about joining in a Brno attack was also arrested.
In another case, a 51-year-old woman was tracked down at her home in Blanensko after allegedly sending police a message in which she praised the Prague shooting.
A third case concerned a threat to ticket inspectors on Prague public transport, with the suspect under investigation despite withdrawing the prank message.
