A 24-year-old student who killed 13 people in a mass shooting at a Prague university is thought to have shot dead a man and his baby daughter in a forest last week in what may have been a dry run for the attack.

David Kozak used an American AR-15 to shoot 27 people in Thursday’s attack before killing himself.

Police chief Martin Vondrasek said the shooter, who killed his father before heading to the Charles University, was the prime suspect in the apparently random murder of a 32-year-old man and his baby daughter near the Czech capital.

“We are working very seriously with the version, which is very real at the moment, that today’s attacker is also responsible for the two victims killed last Friday at Klanovice forest,” Vondrasek said.

Police are also investigating comments apparently left by the Russian speaker on a Telegram account in his name in which he says he took inspiration from a 14-year-old girl who carried out a school shooting in the Russian city of Bryansk on Dec. 7.

Police tightened security at schools and public buildings across the Czech Republic on Friday as crowds thronged to Charles University, where the mourners included Prime Minister Petr Fiala and U.S. Ambassador Bijan Sabet.

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