The suspect in the mass shooting at a Walmart in El Paso “didn’t hold anything back” when he was interviewed by investigators, the city’s police chief said Sunday.

Greg Allen also said “it’s beginning to look more solidly” that the suspect was the author of a manifesto, posted to the website 8chan about an hour and a half before the rampage began, that warns of an “invasion” of Latino immigrants and expresses support for the man who killed worshipers at a mosque in Christchurch, New Zealand, in March.