KYOTO, Japan (Reuters) - Japanese officials groped on Monday for answers to why a blaze tore through an animation company, amid reports that smoke spread so fast a majority of victims who tried to flee through a rooftop door could not open it in time to escape.

One of Japan's worst mass killings in decades, Thursday's attack at Kyoto Animation killed 34 people after a man shouting "die" set ablaze a bucket of petrol he had poured at the building's entrance.