Each year when the Federal Bureau of Investigation releases its statistics on crime, dozens of similar-sounding headlines pop up: “Crime rate down for nth straight year, politician touts policies as reason.”

Just two days ago, Gov. Dannel P. Malloy issued a release about the most recent findings for the state: violent crime dropped by 8.5 percent from 2014 to 2015, leaving Connecticut with its lowest rate since 1974.

“We’re being smart on crime and transforming our criminal justice system — and it’s working,” Malloy said in the release.

But several local criminologists, while they have varying opinions on what’s causing the declining crime rate, agree on one thing: It’s not that simple.

In the United States, the overall crime rate has decreased by 51 percent since 1991, when 5,897.8 crimes were committed per 100,000 people.

In Connecticut, the rate has declined by closer to 62 percent in the same time frame.

To Maria Tcherni-Buzzeo — an associate professor at the University of New Haven Henry C. Lee College of Criminal Justice & Forensic Sciences — that means local policies, while they may have some effect, are not the main factor.

“The declines happened everywhere, in every major city,” Tcherni-Buzzeo said. “Whatever is responsible for the downward trends that began in the early ‘90s, it cannot be a local explanation. It has to be working universally everywhere.”

Tcherni-Buzzeo offered up a few theories about what’s different now than in the early 1990s that could be driving the drop.

For one, she said, changes in the way people communicate likely have led to fewer face-to-face encounters.

She also pointed to the significant increase in the prescription of anti-psychotic and anti-depressant drugs, which began in the early 1990s. Several studies have explored whether such medications, in addition to relieving symptoms, also reduce the perpetration of violence, but none has come up with a definitive answer.

“There are a lot of factors that are interesting to look at,” Tcherni-Buzzeo said.

That’s not to say Tcherni-Buzzeo believes local policies make no difference. She cited Chicago, where violent crime has exploded over the past couple of years, as a place where there’s “clearly something going wrong.”

In a separate interview, John DeCarlo, who also is an associate professor at the Henry C. Lee College of Criminal Justice & Forensic Sciences, pointed to New York City as a place where something is clearly going right.

From 1994, when influential New York City Police Department Commissioner William J. Bratton began his first of two terms, to 2014, crime in the United States decreased by 45 percent. In New York City, it decreased by more than 58 percent.

DeCarlo, citing others who have studied the city, said it’s possible if not likely that policing practices accounted for the additional decrease.

He gave examples of other things that could be causing the country's crime rate to go down, including the ending of the crack epidemic, the aging population and what he referred to as the civilizing effect — an idea championed by cognitive scientist Steven Pinker.

The reduction in crime is “not just a U.S. phenomenon,” DeCarlo said. “But Uruguay, Canada, European countries, they’re also experiencing the drop. Poverty is down, disease is down, education is up ... it’s an evolutionary effect that is driving an increase in civility and a reduction in crime.”

In looking at the 2015 statistics for Connecticut, one will see that of the eight so-called index crimes, all but murder and vehicle theft either remained steady or decreased.

Murders rose more than 31 percent — from 89 in 2014 to 117 in 2015 — while vehicle thefts ticked up about 3.7 percent.

But Ana Campos-Holland, an assistant professor of sociology at Connecticut College, cautioned against drawing any conclusions from one year of change.

“The less information you use to make a point, the more ridiculous that point is,” she said, urging people to look back years, if not decades, for context. “Someone could tell you there’s been a 100 percent increase in something when the number simply rose from one to two.”

Over the past 10 years, the number of murders in Connecticut has fluctuated from as low as 86 to as high as 146. In 2006, it was 108. Ten years before that, there were 158 murders.

“There’s a statistical variation, an ebb and flow of naturally occurring homicides,” DeCarlo said. “When measured against a population of 3.5 million, you’ll see the variation is not as significant statistically. Do we want it to go up? No. But if we look back, we’ll see other fluctuations over the course of the last 15 years.”

Campos-Holland said putting the FBI’s statistics side by side with the Bureau of Justice Statistics’ National Crime Victimization Survey can help paint a fuller picture of crime in the country.

Its numbers are different from the FBI’s — the FBI gathers information from police departments, the Bureau of Justice Statistics from victims — but the latest survey still shows a significant overall decline in criminal victimization since 1993.

“As crime is going down, you’ll see bumps along the way,” DeCarlo said. “Don’t panic.”

l.boyle@theday.com