Mourners gathered outside a Japanese animation studio Friday, one day after 33 people died in a fire that was started by an arsonist. 

Many gathered outside Kyoto Animation Studio to pay their respects to those who died in what is now being considered Japan’s worst mass killing in nearly two decades. 

According to witnesses, a man allegedly screamed “You die!” as he entered the building, poured a flammable liquid and set the structure on fire, Al Jazeera reported. 

The man, who has been identified as Shinji Aoba, was later arrested and remains in the hospital, according to reports. Police said he has "unspecified mental health issues," at a press conference Friday.

"These young people were the age of my grandchildren," 78-year-old Sachiko Konishi told AFP about the deceased. 

Japanese Prime Minister Shinzo Abe called the fire “too appalling for words” in a Twitter post. 

The fire remains under investigation. 

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