ET spoke with the 58-year-old actor in Los Angeles on Thursday, after 70-year-old Simpson was granted parole by the Nevada Board of Parole Commissioners, following nine years in prison for his part in the robbery of two sports memorabilia dealers in Las Vegas in September 2007. Kaelin rose to fame as a witness for the prosecution in Simpson's 1995 murder trial, in which the former NFL pro was found not guilty of the murders of his ex-wife, Nicole Brown Simpson, and her friend, Ron Goldman.
"I've got to say, it's strange to hear his voice. It really is," Kaelin tells ET about watching the parole hearing. "It's that distinctive O.J. voice. It's sort of chilling. And it's a lot of rambling."
"Watching it, I think the biggest shock was that he didn't seem to have the compassion, and the compassion seemed to be with his daughter, Arnelle," he continues, referring to Simpson's eldest daughter, who spoke in support of her father at the parole hearing. "She really spoke from her heart. You could totally tell that she missed her dad. I didn't see the compassion from him. I thought he seemed to be the same O.J. -- just tried and true charisma."
Kaelin -- who stayed in a guest house on Simpson's property in 1994 and was present at the compound on the night of Brown and Goldman's murders -- says Arnelle lived in a guest house next to his and called her a "fantastic person." He also calls Simpson's kids with the late Brown -- Sydney and Justin -- "terrific."
"I think Justin and Sydney are terrific kids," he says, adding that he hasn't spoken to Simpson at all, or anybody involved with the trial. "I think about them, and wonder what they're up to."
Kaelin says he doesn't have any feelings one way or the other about Simpson either staying in prison or becoming a free man.
"I think he's going to have to walk on eggshells the rest of his life," he notes.
Although Simpson repeatedly denied he was seeking media attention during his parole hearing, Kaelin suspects we haven't seen the last of him.
"This will not be the final chapter of O.J. Simpson," Kaelin says. "I think what's going to happen will be either a book deal, a reality show, some sort of sit-down interview, maybe pay-per-view."
He also didn't hold back on his personal thoughts when it comes to Simpson's 1995 "trial of the century."
"I expressed my opinion quite a few times in shows that I think O.J. is guilty of the murders of Ron and Nicole," he says. "That's my opinion, but the jury found him not guilty. I think the jury made a mistake."
"I think O.J. probably is the luckiest man to even be out of prison because, let's face it, in my opinion he got the biggest break of his life, because I thought he was guilty in his murder trial," he continues. "I think getting out of this now, he has to go down to Florida and probably be with his family, be with his kids and never be seen again -- though I don't think that's going to happen."
During his parole hearing on Thursday, Simpson stressed that he wasn't "looking to be involved" with the media should he be released.
"Right now, I'm at a point in my life where I just want to spend as much time with my children and my friends," he said. "I'm not looking to be involved with the media. I'm not interested in any of that. I've done my time. I've done it as well and as respectfully as I possibly can."
ET spoke to Kaelin last February, where he got candid about his gripes when it comes to how he was portrayed in FX's critically acclaimed mini-series, The People v. O.J. Simpson: American Crime Story.
"I think they made a choice of, 'We're going to make Kato Garth from Wayne's World," Kaelin told ET, saying that that the show made him appear to be a stoner. "Can I do anything about it? Absolutely not."