“While New Zealanders and Muslim communities around the world are both grieving and showing compassion for one another, they are also quite rightly asking questions on how this terror attack was able to happen here,” Ardern said Monday, AP reported.

“It is important that no stone is left unturned to get to the bottom of how this act of terrorism occurred and what, if any, opportunities we had to stop it,” Ardern told reporters at Parliament House in the capital, Wellington.

Her Cabinet had previously agreed on holding an inquiry, but had not decided what level of investigation. She said royal commissions are usually reserved for matters of the gravest public importance and that was clearly appropriate in this case. She said the exact terms of the inquiry, including its duration, would be finalized over the next two weeks.

“In short, the inquiry will look at what could have or should have been done to prevent the attack,” Ardern said. “It will inquire into the individual and his activities before the terrorist attack, including, of course, a look at agencies.”

A royal commission is run independently from the government and is chaired by a high court judge. It has the power to compel witnesses to testify and organizations to hand over documents. But it remains up to the courts or government to follow through on any recommendations or findings.

The prime minister ruled out the reintroduction of the death penalty for the accused gunman. The country abolished the death penalty for all offenses including murder in 1961, except for treason and a number of military offenses. The recent mass murder has renewed a debate on whether it was a right decision to scrap the death penalty.

The massacre also prompted an immediate ban on the sales of “military-style” semi-automatic and automatic weapons like the ones used in the mass shooting.

Australian white supremacist Brenton Tarrant, 28, has been charged with murder for the March 15 attack. He is next due in court on April 5.

Some people have already criticized New Zealand's intelligence agencies for focusing too much on perceived threats from Muslims and leftwing radicals but too little on the possible threats from nationalist groups and white supremacists.

“There will be a focus on whether our intelligence community was concentrating its resources appropriately and whether there were any reports that could, or should, have alerted them to this attack,” Ardern said.