Prominent atheist Richard Dawkins has condemned the attack
The man arrested on suspicion of killing three young Muslims in North Carolina described himself as an "anti-theist" and criticised all religions online.
Police said 46-year-old Craig Stephen Hicks handed himself in to officers in Chapel Hill overnight in the wake of the deaths of 23-year-old Deah Shaddy Barakat, his wife Yusor Mohammad, 21, and her sister, Razan Mohammad Abu-Salha, 19.
He has been arrested and charged with three counts of first-degree murder.
23-year-old Deah Shaddy Barakat, his wife Yusor Mohammad, 21, and her sister, Razan Mohammad Abu-Salha, 19. were killed
As tributes poured in for the young family, a Facebook page in Hicks' name showed that he read paralegal studies at Durham Technical Community College and described himself as a supporter of "Atheists for Equality".
A regular social media user, his last three posts were a cute dog video about the Pavlov effect, a viral advert for Air New Zealand involving mountain bikes, and a picture from United Atheists of America asking "why radical Christians and radical Muslims are so opposed to each others' influence when they agree about so many ideological issues".
TV programmes liked by Hicks include The Atheist Experience, Criminal Minds and Friends, while he describes himself as a fan of Thomas Paine's The Age of Reason and Richard Dawkins' The God Delusion.
Hicks posted this picture with the caption: 'Yes, that is 1 pound 5.1 ounces for my loaded 38 revolver, its holster, and five extra rounds in a speedloader'
This picture shows Hicks on holiday with his wife in Disneyland
Hicks read paralegal studies at Durham county's Technical Community College
Hicks' pictures largely consist of images with text mocking religion and supporting atheism, but include images of himself and his wife at Disneyland, what he describes as his "loaded 38 revovler", and himself separately on a quad bike and wearing a suit.
The shooting of the three Muslims has been widely condemned across social media, including by Richard Dawkins himself, who tweeted: "How could any decent person NOT condemn the vile murder of three young US Muslims in Chapel Hill?"
Other users have called on people to donate to a charity in Deah Barakat's honour. The victim volunteered for a number of agencies providing dental relief to Syrian and Palestinian refugees, as well as caring for homeless people in the US.