San Antonio’s overall crime rate in 2017 decreased to its lowest level in at least three decades, but it remains the highest among the nation’s 15 largest cities, including Houston, Dallas and Austin.

There were 5,552 crimes reported per 100,000 residents in San Antonio, according to 2017 data released Tuesday by the FBI. That rate includes the eight crimes that the FBI considers the most serious — homicide, rape, robbery aggravated assault, burglary, larceny/theft, motor vehicle theft and arson.

That’s a decrease from 5,908 crimes per 100,000 in 2016. Thirty years ago, the rate was more double that.

Explanations of ups and downs in crime rates are difficult to come by.

“I wish we had the definitive answers,” said Robert Taylor, a professor of criminology and public affairs at University of Texas at Dallas. “Criminologists are pretty baffled right now about what causes crime.”

There were 10,759 violent crimes reported in San Antonio last year. While the number is similar to 2016, the per capita violent crime rate decreased in 2017, due mostly to the city’s growth. Violent crime includes homicide, rape, robbery and aggravated assault. It does not include justified homicides or officer-involved killings.

There were 708 violent crimes per 100,000 people in 2017, the data shows, down from 718 the year prior.

Experts say it’s normal for crime to fluctuate from year to year, sometimes without an apparent cause.

In the past, criminologists have tied high crime rates to a variety of factors, including high unemployment rates and concentrated poverty. But Taylor said those theories have been discredited in recent years.

“In the last two decades, we saw a decrease in crime even though we had problems with our economy,” he said. “Now we’re seeing an uptick in crime. We can’t tie it to economic decline because our economic engines are doing really well right now.”

There were 124 homicides reported in San Antonio last year, a 17 percent decrease from the year prior, when homicides reached a 21-year high. Still, 2017 was the second deadliest year since 1995. Last year’s total included the deaths of 10 migrants who were trapped in a tractor-trailer while they were being smuggled into the U.S. They were found in a parking lot on the South Side.

The data released Tuesday is part of the FBI’s Uniform Crime Reporting Program, which is a compilation of crimes reported by law enforcement agencies from across the nation. While the data does have shortcomings, it provides an overall picture of crime and how San Antonio compares to other cities.

An Express-News analysis of the data shows:

There were 73,676 property crimes reported in San Antonio last year, a 5 percent decrease from the year prior. The rate for property crimes — which includes burglary, larceny/theft, motor vehicle theft and arson — also decreased from 5,190 per 100,000 to 4,845.

For the second year in a row, the violent crime rate increased in over half of the region’s municipalities — most notably in Converse, Universal City and Leon Valley. The violent crime numbers are still fairly low in comparison with large cities, and most of the agencies — besides San Antonio — reported very few homicides. Some reported zero.

On Tuesday, Taylor said he imagines what really impacts crime is dependent on local variables, like police-community relations and policing techniques.

“How well is the police department perceived in the community?” he said. “How aggressive are they, not in a violent way, but in pulling people over and trying to thwart criminal activity? How much activity do they have in the community?”

A spokeswoman for the San Antonio Police Department declined to comment on the FBI data, saying she was unable to get to the request.

In the past, Police Chief William McManus has said that most crime in the city could be credited to “risky behavior” — people who engage in drug deals, partake in gang activity or deal with criminals.

Earlier this year, McManus said an unnamed East Side gang was responsible for much of that area’s violent crime.

He unveiled the Violent Crime Task Force in collaboration with several federal and state partners. In the task force’s first 10 months of operation, the agencies made 4,175 arrests — a figure equating to about 14 arrests a day, from January 2017 to October 2017.

“We targeted specific gang members and gutted them,” McManus said in January.

In the past, McManus has cautioned against using the data to compare cities because agencies aren't required by law to submit statistics to the FBI program. Additionally, even though the UCR program tries to standardize crime classifications, definitions can vary from jurisdiction to jurisdiction.

“I think the headline that says that San Antonio is the most dangerous city in the nation is misleading,” he said last year. “There are a lot of cities that have been considered dangerous for years, and San Antonio is not one of those.”

This story has been corrected to reflect the proper violent crime and property crime rates.

Emilie Eaton is a criminal justice reporter in the San Antonio and Bexar County area. Read her on our free site, mySA.com, and on our subscriber site, ExpressNews.com. | eeaton@express-news.net | Twitter: @emilieeaton