Wellington, March 27 -- The man who committed the worst atrocity in New Zealand's modern history when he slaughtered 51 worshippers at two Christchurch mosques unexpectedly pleaded guilty to all charges Thursday.

The attacks targeting people praying at the mosques a year ago shocked the nation and prompted new laws banning the deadliest types of semi-automatic weapons. The sudden turn in the case took survivors and relatives by surprise, and brought relief to people across New Zealand. Many had feared Australian white supremacist Brenton Harrison Tarrant would try to use his trial as a platform to promote his views. He'd outlined those views in a 74-page manifesto he published online shortly before the attacks.

Tarrant, 29, pleaded guilty...