Despite a grinding recession, reported crime in the United States continues to fall, the FBI said Monday.

Violent crime was down 6 percent in 2010 - the fourth consecutive yearly decline, according to the FBI's Uniform Crime Report.

Property crime dropped for the eighth year in a row, down 2.7 percent in 2010.

In Pennsylvania, violent crime fell 3 percent and property crime ticked down 0.5 percent.

New Jersey and Delaware reported small drops in violent crime, but increases in property crime.

"Everyone anticipated the recession would drive things up, and it hasn't happened," said Alfred Blumstein, a professor at Carnegie Mellon University's Heinz School of Public Policy.

Crime trends are easier to discern after a number of years have passed.

The spread of crack cocaine in the late 1980s into the early 1990s saw an epidemic of violence.

Smarter policing methods developed in New York in the early 1990s played a role in reducing it, as did the large numbers of people sent to prison.

Around 2000, crime statistics leveled at historic lows and stayed there for several years.

"Maybe it was as low as it could go," Blumstein said, echoing an observation made by many criminologists.

Trying to figure out why crime is not spiking during this period of high unemployment and general economic misery would be "pure speculation," Blumstein said.

The number of sworn law enforcement officers has fluctuated, shrinking since 2008, before which it had grown substantially, according to the FBI report.

That decline coincides with government agencies struggling to maintain services while suffering from declining tax revenue.

The number of reported arrests nationally has dropped substantially in recent years, from 14.4 million in 2006 to 13.1 million in 2010.

A drop in the number of arrests could be attributable to a number of factors, and not simply because there were fewer reports of crimes.

Blumstein noted that the numbers of blacks arrested had dropped noticeably more than the numbers for whites.

"I was struck by the difference," he said.

He speculated that there might be an "Obama effect" keeping some African Americans away from crime. "Pure speculation," he cautioned again.

Homicide numbers are difficult to fudge. Pennsylvania recorded a slight drop, and New Jersey and Delaware had increases in murder and nonnegligent manslaughter, which is how the FBI defines the category.

All three states reported declines in forcible rapes.

The FBI reported that there were an estimated 1,246,248 violent crimes and 9,082,887 property crimes in the United States in 2010.

The national violent crime rate per 100,000 people was 403.6.

Pennsylvania's rate was 366.2. In New Jersey, the rate was 307.7. In Delaware, the rate was 620.9.

Contact staff writer Robert Moran at 215-854-5983, bmoran@phillynews.com, or @RobertMoran215 on Twitter.