When the echo of gunfire stilled in Christchurch that awful day, one of Facebook's most senior executives was quick to present the company as a willing solution to the massacre it had broadcast live.

"My deepest condolences for the attack that took place yesterday," wrote chief operating officer Sheryl Sandberg at 6.39am, the morning after the March 15 attack, to Prime Minister Jacinda Ardern.

"It's absolutely heartbreaking. I'm keeping the people of New Zealand in my thoughts and wishing you all strength during this difficult time.

The email - one of many released through the Official Information Act - would


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