Karen Hicks said she was “shocked” by the attack but said her husband Craig, 46, had parking disputes with many neighbours, of all religions.
Deah Barakat, his wife Yusor Mohammad Abu-Salha and her sister Razan Mohammad Abu-Salha were found dead, shot in the head at home in North Carolina.
Their family has said the attack in Chapel Hill was motivated by hate.
Mohammed Abu-Salha, father of the two sisters who were killed, said Mr Hicks had killed them “execution style”.
“This man had picked on my daughter and her husband a couple of times before, and he talked with them with his gun in his belt,” he told the News-Observer newspaper.
“And they were uncomfortable with him, but they did not know he would go this far.”
On Wednesday, the wife of Mr Hicks, Karen Hicks stood alongside a lawyer as she told reporters her husband believed “everyone is equal, it doesn’t matter what you look like, who you are or what you believe”.
Deah Barakat, 23, second-year dental student (above with bride Yusor)
Yusor Mohammad Abu-Salha, 21, due to start dental studies in autumn
her sister Razan Mohammad Abu-Salha, 19, a second year student
Her lawyer said the shooting had “nothing to do with the victims’ religious beliefs but had everything to do with a mundane parking spot dispute”.
The lack of access to mental health care was the real issue, he said, not terror.
Chapel Hill Police said in a statement there had been an ongoing parking dispute but they are still investigating whether the attack was hate-motivated.
Mr Hicks’ Facebook profile included a photo that read “Atheists for Equality”. He frequently posted quotes critical of religion.
He had also posted a photo on 20 January of a gun he said was loaded and belonged to him.