WASHINGTON - Crime levels fell across the board last year, extending a multi-year downward trend with a 5.5 percent drop in the number of violent crimes in 2010 and a 2.8 percent decline in the number of property crimes.

Year-to-year changes released Monday by the FBI in its preliminary figures on crimes reported to police in 2010 also showed declines in all four categories of violent crime in 2010. All categories for property crime went down as well.

"In a word, remarkable," said James Alan Fox, a criminologist at Northeastern University. In Fox's view, the declines signify success for aggressive law enforcement and corrections programs and comprehensive crime prevention efforts. He said the crime levels could easily rise if the current environment of state and local budget cutting extends to law enforcement measures that are working.

Some experts are puzzled.

Expectations that crime would rise in the economic recession have not materialized. The size of the most crime-prone population age groups, from late teens through mid-20s, has remained relatively flat in recent years.

"I have not heard of any good explanations for the good news we've been experiencing in 2009 and 2010," said professor Alfred Blumstein of Carnegie Mellon University's Heinz School of Public Policy. "I hope the trend continues and I'm going to keep searching for answers."

Violent crime last increased in 2005. Property crime last increased in 2002.

The FBI reported that violent crime fell in all four regions of the country last year - 7.5 percent in the South, 5.9 in the Midwest, 5.8 percent in the West and 0.4 percent in the Northeast.

The bureau's preliminary statistics for 2010 are based on data from more than 13,000 law enforcement agencies nationwide.

Nationally, murder and non-negligent manslaughter declined 4.4 percent, forcible rape decreased 4.2 percent, robbery declined 9.5 percent, and aggravated assault was down 3.6 percent.

The downward trend for murder and non-negligent manslaughter was especially pronounced in the nation's smallest cities, where it went down 25.2 percent for cities under 10,000 people. Murder actually rose 3 percent in cities with populations of 250,000 to half a million. In New York City, the number of murders and non-negligent manslaughter cases rose from 471 to 536, up 13.8 percent.

Among property crimes, motor vehicle theft showed the largest drop in 2010 - 7.2 percent - followed by larceny-theft, which was down 2.8 percent and burglary, a decline of 1.1 percent.

FBI crime data: http://tinyurl.com/3vdb3z7