The U.S. crime rate has dropped to the lowest level in 30 years, surprising many experts.

A study released Sunday by the Bureau of Justice Statistics said that property crimes and violent crimes, except for murder, decreased to about 23 million last year. That compares with 44 million victims in 1973, the first year the government began recording crime data. The study found crime down in cities, suburbs and rural areas, across all racial, ethnic and income lines.

The study did not examine murders, which are measured separately by the FBI. Preliminary reports from the FBI indicate that the number of murders increased slightly last year.

Some experts had expected violent and property crime rates to increase because of higher unemployment and budget cuts in towns and cities. Criminologists attribute the long-term plunge to a number of factors, including a drop in gang membership, an aging population and tougher prison sentences. Violent crimes are predominantly committed by young males.

The United States' jail and prison population swelled to more than two million last year, an all-time high.