Washington (CNN) -- Violent crime dropped nationwide last year, continuing a downward trend of more than a decade, new FBI statistics show. 
 
 But in towns with populations under 10,000, murders saw a big jump. 
 
 Overall, violent crime was down 4%, according to the Preliminary Annual Uniform Crime Report for 2011. 
 
 Numbers dropped in all categories nationwide. Murders fell by 1.9%, while rapes, robberies and aggravated assaults declined 4%. 
 
 But the figures, provided by police agencies, show that murders jumped 18.3% in small towns of under 10,000. 
 
 Property crime decreased slightly in 2011 -- down 0.8% overall. 
 
 Burglaries stayed almost even across the country, rising just .03% from the previous year. But they were up 3.2% in the Northeast and 1.3% in the Midwest. 
 
 The FBI report does not give reasons for the continuing decline. 
 
 CNN's Terry Frieden, Melissa Abbey and Josh Levs contributed to this report. ||||| Violent crime rates in the U.S. are reaching historic lows, according to new FBI data released Monday. 
 
 Instances of murder declined overall by 1.9 percent from 2010 figures, while rape, robbery and aggravated assault declined by 4 percent nationwide, according to records from more than 14,000 law-enforcement agencies around the country, FBI spokesman Bill Carter told msnbc.com. 
 
 The number of property crimes also registered a 0.8-percent drop, motor-vehicle thefts declined by 3.3 percent, and arson was down by 5 percent. 
 
 Although the findings, released in the FBI’s Preliminary Annual Uniform Crime Report, represent a seemingly small decline in crime overall, they aren’t just a blip. Rather, criminologists say, the decline is part of larger downward trend and the result of a series of changes that have contributed to a more peaceful society. 
 
 “This is actually a pretty significant drop, which is fascinating because we’d normally expect crime to go up when we’re in an economic downturn,” Gary LaFree, a criminology professor at the University of Maryland, told msnbc.com, adding that the U.S. is experiencing the lowest crime levels since World War II. 
 
 According to FBI analysis, the homicide drop would mean that nearly 280 fewer Americans were murdered last year, which would be the lowest homicide death toll since the mid-1950s. 
 
 LaFree said a combination of factors – from a weak economy and an aging population to increased immigration and a more robust police presence across the country – have contributed to the drop. 
 
 “One of the responses of society is to pull together when there’s a huge crisis and a feeling of great difficulty,” LaFree said, adding that the economic climate may have contributed to this peaceful trend. 
 
 Additionally, with the current U.S. median age at 37.2 years, older than ever before, the aging population is another possible cause, LaFree said. “There is some truth to the fact that younger people commit more crimes,” he said. 
 
 “We also have a record number of immigrants, and contrary to popular belief,” LaFree said, “immigrants have lower crime rates than the rest of society.” 
 
 But some argue the data may not signify such remarkable changes. 
 
 “Year-to-year changes are notoriously volatile, especially for lesser-volume crimes like murder,” James Alan Fox, a criminologist at Northeastern University in Boston, wrote in his blog. “They must be viewed with caution, avoiding the temptation to make too much out of rather little.” 
 
 Fox said it’s possible the long-term downturn in crime has slowed and even bottomed out. 
 
 Still, LaFree argued there’s a reason the numbers indicate what they do. 
 
 “Compared to years ago, “There’s nothing that’s ripping apart the fabric of society in a political sense,” LaFree said. 
 
 The mass protests during the Vietnam War and the beginnings of crack cocaine epidemic contributed to more violent crimes in the past, LaFree said. He said he thinks there are fewer problems as extreme as either of those in society today. 
 
 As for the serious crimes that do occur, there exists a strong deterrence factor in the prison system, despite debates about its effectiveness, he said. 
 
 But more importantly, LaFree said, there has been a “quiet revolution” in law-enforcement policy over the past few years. 
 
 “Police departments have become much more proactive across the country,” Lafree said. “They used to deploy resources to handle crime, but now they’re much more likely to target problems beforehand and emphasize a solution.” 
 
 Fox, however, warned against resting on news that could be seen as too positive. 
 
 “With rates relatively low, this is not the time to diminish crime fighting-efforts,” he said. “If we naively presume that the crime problem has been solved (as opposed to just controlled for the time being), the crime rate could easily rebound.” 
 
 The FBI's final crime figures will be released this fall. 
 
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– The violent crime rate in the US dropped for the fifth straight year in 2011, and is approaching a low not seen in decades, according to new FBI data. The overall violent crime rate fell 4%, with murders down 1.9%, and rapes, robberies, and aggravated assaults down 4%—although murders in small towns with fewer than 10,000 people surged 18%, CNN reports. Despite the economic downturn, property crimes like burglary were down 8%, a small decline but the ninth consecutive annual one, Reuters notes. The fall in violent crime is because of a combination of factors, including better policing, an older population, and the tendency of communities to pull together when faced with a crisis like the economic downturn, a University of Maryland criminology professor tells MSNBC. "We also have a record number of immigrants, and, contrary to popular belief, immigrants have lower crime rates than the rest of society," he says. But the FBI figures show that violent crime began to edge upward toward the end of 2011, and experts warn that the low crime rate should not cause agencies to ease crime-fighting efforts.