The number of apprehensions of people for federal immigration violations has dropped to its lowest level in 40 years, reflecting a decline in the northbound traffic of illegal immigrants from Mexico, according to a government report released Wednesday. 

The report, released by the U.S. Bureau of Justice Statistics, said such apprehensions stood at 1.8 million in 2000, but declined dramatically to 516,992 in 2010, the lowest level since 1972. 

"Most people don't want to leave (their home county)," said Lisa Garcia Bedolla, a University of California-Berkley social and cultural studies associate professor. "Things aren't that bad in the Mexican economy right now."

Meanwhile, arrests for criminal immigration offenses are rising. Suspects arrested by the U.S. Marshals Service for federal criminal immigration offenses increased from 8,777 in 1994 to 82,438 in 2010. 

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Most arrests and apprehensions in 2010 were concentrated on the Southwest border sectors. 

The most common offense, according to the report, is illegal re-entry followed by alien smuggling and misuse of visas. 

Mexican citizens made up 83 percent of deportable aliens in 2010, down from 94 percent in 2002. 

Read the full report here

However, the number of deportable aliens coming from Central America increased from 3 percent to 12 percent during an eight-year period ending in 2010.  

The number of Border Patrol officers doubled from 10,819 in 2004 to 20,558 in 2010, with most located along states that abut Mexico.  

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The study classifies immigration apprehension as a case where a foreign national is caught in the U.S. illegally, while an arrest refers to the booking of an individual by the U.S. Marshals for violating federal immigration law.

Both terms represent events rather than individuals because a person can be apprehended or arrested more than once, the report explains.

NBC News' Louis Casiano contributed to this story.

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