Facebook has launched a review into how it deals with violent content on its network.
The announcement came after a video showing a killing was posted to Facebook on Sunday and remained there for more than two hours.
"We know we need to do better," a company executive said.
Police were still looking for the suspect in the shooting, Steve Stephens.
The 37-year-old posted a video showing the fatal attack on 74-year-old grandfather Robert Godwin, who was picked apparently at random.
Later Mr Stephens took to Facebook Live to discuss the killing, saying he had killed 13 people - though police said they were unaware of any other deaths.
Facebook has faced considerable criticism due to the length of time the violent video spent published on the network.
"As a result of this terrible series of events, we are reviewing our reporting flows to be sure people can report videos and other material that violates our standards as easily and quickly as possible," wrote Justin Osofsky, Facebook's vice-president of global operations.
"In this case, we did not receive a report about the first video [which featured the suspect saying he intended to murder], and we only received a report about the second video - containing the shooting - more than an hour and 45 minutes after it was posted.
"We received reports about the third video, containing the man's live confession, only after it had ended."
Mr Osofsky pointed out that the video showing the killing was on Facebook for an hour and forty-five minutes before it was flagged by a user. The video, and the user account, was taken down 23 minutes later, according to Facebook's statement.
The company said as well as human moderation, artificial intelligence would be a useful tool in combating the sharing of this kind of material.
Facebook's annual developers' conference takes place in San Jose, California, on Tuesday and Wednesday this week.
Mark Zuckerberg will open the event with a keynote address - though it is not yet known if he will address this controversy.
What was reported when:
11:09AM PDT (19:09 GMT) - first video, of intent to murder, uploaded. Not reported to Facebook.
11:11AM PDT - second video, of shooting, uploaded.
11:22AM PDT - suspect confesses to murder while using Live, is live for 5 minutes.
11:27AM PDT - Live ends, and Live video is first reported shortly after.
12:59PM PDT - video of shooting is first reported.
1:22PM PDT - suspect's account disabled; all videos no longer visible to public.