Some legal experts questioned the addition of the terrorism charge, saying it increased the chance that the gunman — a self-proclaimed white supremacist who posted a rambling manifesto online and streamed part of the massacre live on Facebook — would be able to use the trial as a platform for his ideology.

“He will say ‘I’m not a terrorist, I’m a patriot,’” Bill Hodge, a University of Auckland law professor, told Newstalk ZB, adding that the suspect could invoke his views in explaining why he had not committed terrorism.

Local news outlets in New Zealand have agreed on a set of guidelines for reporting on the case if it goes to a trial; they include not reporting on white supremacist views. Mr. Tarrant, who had earlier said he would represent himself in court, now has lawyers acting on his behalf.

Mr. Tarrant has yet to enter a plea on the charges; at his last court appearance, in April, a judge ordered psychiatric reports to ensure his fitness to stand trial, a normal procedure in New Zealand murder cases. He will next appear in court in June.

No one has ever been sentenced to life without the possibility of parole in New Zealand; the longest previous sentence for murder was 30 years without chance of release for a man convicted of a triple murder. A judge has the discretion to remove the possibility of parole if Mr. Tarrant is found guilty.