Steinberg criticized Deputy District Attorney Chris Gallo and Assistant District Attorney Bob Chappell for not calling Vaughn to the witness stand to explain his statement about "girl on girl action."
"Where is he? Steinberg asked the jury during closing arguments. "Are they afraid of the truth?"
Afterward, Gallo said he didn't believe Vaughn's testimony was essential to their case.
"There are certain things that we have to prove and we put on the evidence that we thought would prove" our case, he said. "What goes on in a jury room, for a very good reason, nobody really knows."
Vaughn did not return a message left by The Associated Press.
Cox, 25, was a rookie out of Oklahoma State who had played eight games for the Broncos when he was arrested.
His legal troubles capped a tumultuous time for the Broncos, who had dealt with the drive-by slaying of cornerback Darrent Williams on New Year's Day 2007, running back Damien Nash's fatal heart attack in March 2007 and receiver Kenny McKinley's suicide in September 2010.
Cox's agent, Jordan Woy, said he has spoken to several interested NFL teams.
"We expect for him to move forward in his NFL career," Woy told The Associated Press in an email. "Perrish is looking forward to focusing on his life both personally and professionally."
The Broncos said they had no comment on the verdict since Cox no longer is with the organization.
Associated Press Sports Writer Pat Graham contributed to this report.
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.