None of the 200 people who watched the live video of the Christchurch massacre reported it immediately to Facebook during the attack.
It also took half an hour after Brenton Tarrant started his live video for anyone to report it using Facebook's reporting tools.
Facebook vice president Chris Sonderby said the social media giant is working around the clock to prevent the video from being shared again.
"The video was viewed fewer than 200 times during the live broadcast. No users reported the video during the live broadcast," Mr Sonderby said in a statement on Tuesday.
"Including the views during the live broadcast, the video was viewed about 4000 times in total before being removed from Facebook.
"The first user report on the original video came in 29 minutes after the video started, and 12 minutes after the live broadcast ended."
The link to the live-stream was posted on anonymous message board 8chan, and shortly after the 17-minute video ended, a download link for it was also posted on the site.
Facebook removed the video and "hashed" it to automatically prevent it being uploaded again, but some users added watermarks or edited the video in order to slip it past the detection algorithms.
In the first 24 hours after the shooting, Facebook removed about 1.5 million versions of the attack video.
"More than 1.2 million of those videos were blocked at upload, and were therefore prevented from being seen on our services," Mr Sonderby said.
Prime Minister Scott Morrison has asked G20 members to consider practical ways to force companies like Facebook and Google to stop broadcasting atrocities and violent crimes.
Mr Sonderby said Facebook is committed to working with leaders in New Zealand and other governments to help counter hate speech and the threat of terrorism.
