In an exclusive interview with RadarOnline.com, Grace said she believes Simpson's aggressive online behavior proves who he really is when he's not hiding behind a computer screen.
"What do you expect O.J. Simpson to do besides get right on Twitter and say, 'I got a lot of getting even to do.' That's his nature," the respected legal analyst said.
As RadarOnline.com reported, Simpson joined Twitter just hours after the 25th anniversary of the murders of his ex-wife Nicole Brown Simpson and her friend Ronald Goldman. Days later, the former NFL player tweeted that he wanted to "get even" with naysayers and would "cut" a man who started a parody social media account about him.
"Think I'm playing motherf***er..." Simpson allegedly wrote under The Juice's new Twitter handle @TheRealOJ32.
"Sadly, nope," responded parody account @KillerOJSimpson, who posted a video of the disturbing exchange.
"Seen that video just posted about me. You think I'm playing? Tired of all your bulls**t. I WILL FIND YOUR A** AND CUT YOU. Don't believe me? Just watch and see b***h," @TheRealOJ32 allegedly fired back.
"To me, it just reinforces the fact that he's a double killer. That's just who he is," Grace told RadarOnline.com.
Simpson was infamously acquitted of the gruesome June 12, 1994 killings of his ex-wife Nicole Brown Simpson and her friend, Ron Goldman. He was later convicted of armed robbery in 2008 and served nine years in a Nevada prison before being released on parole in 2017.
Grace, who is gearing up for the premiere of her new show, Injustice with Nancy Grace on Oxygen, also slammed the former murder suspect's post-prison lifestyle.
"Most people would be kissing the ground that they're out of jail. He's living in a mansion, he's golfing every day, he's having all these women writing letters to try to date him," the veteran prosecutor said. "He's treated like a celebrity."
"But what does he do instead of thanking God for being free again? He's basically sending out threatening tweets," Grace continued. "It never ends with him. It never will."
"He is compelled to lash out," Kim told RadarOnline.com.
However, The Blast reported from sources that the video exchange was fake.
Despite the Twitter chaos, Grace focused the attention back on the murder victims.
"Can you imagine poor Nicole Brown having to live with him?" the TV host said.
Grace's new show, Injustice with Nancy Grace, premieres on the Oxygen Network on Saturday, July 13 at 6 p.m. ET. The legal eagle said the show will zero in on crimes she has not yet commented on before.
"These are cases that have not been raked over the coals and analyzed ad nauseam," Grace explained. "These are cases that many people have never heard of."
Grace added that she hand picked each case she plans to explore on the Oxygen show.
"Each one represents something very critical to our justice system," she said.