Few details have emerged about Mr. Tarrant’s life. It is unclear whether he had a job. Several neighbors said they did not know many of their neighbors and had not met Mr. Tarrant.

Anytime Fitness confirmed in a statement on Monday that Mr. Tarrant was a member of the Dunedin branch of the 24-hour gym. On Sunday, several regulars at the gym said they did not know Mr. Tarrant or recall seeing him there.

What is known is that Mr. Tarrant was a licensed gun owner and member of the Bruce Rifle Club. He appeared to already have shooting skills when he joined in February 2018 and he typically went to the range by himself, said Mr. Williams, the club’s vice president.

The club has come under criticism from a former member of the New Zealand military named Pete Breidahl, who said he reported it to the police in 2017 after visiting in November that year. He said he had had concerns about the mental stability of the members and the way they handled firearms.

“They wore camo around the range, like they were living some military base fantasy,” Mr. Breidahl said in an interview on Monday.

Mr. Breidahl said that he had been in contact with the police after the Christchurch shootings and that he was scheduled to meet with them on Tuesday.