Grieco said the "whole thing is a fabrication" during a radio interview Monday on Sports Radio 950 KJR (via Curtis Crabtree of Pro Football Talk).
"It's a fabrication," he said. "I wouldn't be coming out as quickly and as loudly as I have if I didn't strongly believe that that's the case. Everything that's happened since that day has just further buttressed my position on that."
Grieco explained he's obtained four sworn affidavits from witnesses that contradict their original allegation that Dunbar was involved in an armed robbery in Florida.
"Whether I'm being told the truth or the police are being told the truth, those two stories are completely different," he said. "They've sworn under penalty of perjury to both versions of events. So when I say they're liars, they're liars. They either lied under oath to me or they lied under oath to the police. Either way, their credibility is shot."
The police report filed as part of an arrest warrant for Dunbar and New York Giants cornerback DeAndre Baker alleged Baker was telling two people, including Dunbar, to take "money and valuables" from people attending a party Wednesday while he brandished a gun.
One witness told police he'd met the NFL players a few days earlier at a separate party and witnessed them lose "about $70,000."
TMZ Sports reported Tuesday police have been unable to obtain video of the alleged heist, which investigators were told included $72,000 in stolen cash and watches.
Grieco said the notion witnesses have changed their story because of duress or coercion is "ridiculous," per Crabtree.
Dunbar and Baker turned themselves in to police Saturday and are now out on bond on four counts of armed robbery.