The number of crimes reported to police dropped again last year compared with 2010, but a closer look at the numbers suggests the long annual line of declines in crime levels may have hit bottom.

Last year marked the fifth straight year of year-to-year improvement for the number of violent crimes reported to authorities. It was the ninth consecutive year of declines for property crimes, according to preliminary FBI data for 2011 released Monday.

However, the early 2011 figures show that the decline in both violent crime and property crime levels slowed from July through December of last year. Violent crime fell 6.4 percent in the first six months of last year. But for the entire year, the decline was much less, just 4 percent. The number of reported property crimes fell 3.7 percent in the first half of last year. For all of 2011, it went down 0.8 percent.

"The picture for January to June looked terrific," said Northeastern University criminology professor James Alan Fox. "For the entire year, it's very different. Maybe we're reaching the end of the trough in declining crime levels. It's what happened in the second part of the year that concerns me."

The FBI says murder and non-negligent manslaughter, rape, robbery and aggravated assault all went down in 2011.

Violent crime decreased in all four regions: 4.9 percent in the Midwest; 4.7 percent in the West; 4.5 percent in the South and 0.8 percent in the Northeast.

There was, however, an increase in murder in the Midwest — 0.6 percent — and an 18.3 percent jump in murder in cities with populations of less than 10,000.

In the property crime category, motor vehicle theft dropped 3.3 percent, and larceny-theft decreased 0.9 percent. However, burglary offenses increased 0.3 percent, rising 3.2 percent in the Northeast, 1.3 percent in the Midwest and 0.7 percent in the West.

The preliminary data is based on information the FBI gathered from 14,009 law enforcement agencies around the United States.