Ms. Viccaro, 22, of New Milford, had been charged as one of two accomplices in the robbery at a Webster branch along the Village Green in New Milford.
The robbery netted about $2,000 and led to the incarceration of Preston Hanlon, 29.
Mr. Hanlon told police and jurors at Superior Court in Litchfield that Viccaro and he saw themselves as a "Bonnie and Clyde" team, planning the robbery together.
Ms. Viccaro maintained her innocence from the time of her arrest.
"The jury got the case for deliberation a little after 2 p.m. (Oct. 3)," said Ms. Viccaro's attorney, Murray Kessler.
"At 4 p.m., they asked for a reading of Mr. Hanlon's testimony. They were looking to see if there were any contradictions which would give them an idea if it was the truth."
The jurors heard the last of the reading of Mr. Hanlon's testimony the morning of Oct. 4.
Mr. Kessler said they were back with their verdict within 20 minutes of returning to deliberations.
"It became very obvious that Mr. Hanlon was changing his story, back and forth," Mr. Kessler said. "They had a chance to see his veracity and found it was wanting.
"This was not a case where there was not enough evidence to find Ms. Viccaro guilty beyond a reasonable doubt," he added. "There was no evidence.
"The jury couldn't get past the point that she didn't do anything wrong," he said. "Serena was totally vindicated."
A call to state's prosecutor David Shannon for comment was not returned.
Mr. Hanlon is serving a 15-year prison sentence, to be suspended after five years, on a conviction of first-degree robbery in the crime.
His former roommate, Micah Theisz, 26, has also been charged as an accomplice. Mr. Theisz' case is pending.