NewsChannel 5 Investigates asked Serpas before his resignation, "Unprecedented? How much of that is spin?"
"It's fact," the chief answered emphatically.
It's a claim that was repeated by Mayor Karl Dean even as Serpas announced that he was leaving Nashville to take the top cop job in his hometown of New Orleans.
The police department's own stats, tracking seven major crimes, show that crime dropped in 2004 after Serpas arrived and continued to drop year after year after year. Included in that was 2005, a year that saw a rash of murders, robberies and other violent crimes.
"We have been using the uniform crime report since 1963 to report the major crime rates in Nashville," Serpas said. "We have not changed that."
But the FBI says crime actually went up two of those years.
Tracking the same seven crimes that Metro says it tracks, the FBI's own stats show Nashville's crime dropped in 2004, followed by a slight uptick in 2005. It dropped for the next two years.
But in 2008, the FBI says crime went up again -- although, as Serpas noted, the formula that the FBI uses has always come up with a fewer number of total crimes.
"I don't go back and say let's take this new lower number," he said. "We take the number that we think we've counted. We don't take the FBI's number."
Still, NewsChannel 5 Investigates noted, "When the FBI analyzes your data, they have a very different trend line than what you have."
"It's the first that I've seen it in that way," Serpas responded.
Then, there are Metro's own reports to the TBI, using a more advanced system that tracks even more types of crime. Serpas calls it a "more sophisticated" measurement.
TBI's stats show Nashville crime was essentially flat in 2004. But TBI also shows an increase in 2005, down in 2006. Then in 2008, the TBI also says crime headed back up.
NewsChannel 5 Investigates asked, "When you are reporting one set of numbers and the FBI and TBI are reporting an entirely different trend, how is the public supposed to know whether to believe you or not?"
Serpas answered with his own question about the statistics, pointing to one case where his department showed a tiny decrease in one category.
"Why would anybody assume we just was making them up?"
Which brings us to a Metro Council meeting in 2009 where Serpas presented his 2008 crime stats -- stats that once again claimed overall crime was down.
Serpas told the public that burglaries were flat, that aggravated assaults were down, that rapes were down, that larcenies were down.
Yet, the FBI and TBI both say all of those were up.
"Yes," Serpas answered, "but they also report fewer than we did. So why are you immediately jumping to the conclusion that either one of us is necessarily wrong?"
NewsChannel 5 Investigates asked, "How is the public supposed to know who to believe?"
"Well," the chief responded, "why are we immediately jumping to the conclusion that they are right and we are wrong?"
Metro Councilman Jim Gotto said he's not jumping to any conclusions.
Gotto drew the chief's ire during that meeting when he suggested that -- because of rumors that Serpas was spinning the numbers -- he ought to get an independent audit.
Serpas told NewsChannel 5 Investigates, "You and I both know that the police department has been audited four times in the last six years -- three times by TBI and once by the FBI."
But TBI says it can only vouch for TBI stats -- not the ones Serpas used.
"The only thing that we audit are the crime stats that come to TBI directly," spokesperson Kristin Helm said. "I don't know what other agencies present to their mayors to their council -- anything like that."
Gotto said that's why an independent audit is needed.
"Again, I'm not accusing anybody of any wrongdoing," Gotto added. "I don't know whether we are doing it right or not. All I'm saying is there is a fairly simple way I think to really get at this once and for all and put it to rest."
But Serpas insisted, for the public, it should come down to this: "I think they've just got to take a leap of faith."
We also found an internal report comparing crime in 15 cities. Nashville was sixth out of 15 in terms of violent crime - far worse than cities like Louisville, Charlotte and Jacksonville.
But it was right behind cities like Memphis, Atlanta and Miami.