Crimes across the United States are divided into two categories, Part I and Part II, using the Uniform Crime Reporting (UCR) System. The International Association of Chiefs of Police developed the UCR program in the 1920's and since 1930, the FBI has collected and compiled the data.
The UCR Program collects offense information for murder and non-negligent manslaughter, forcible rape, robbery, aggravated assault, burglary, larceny-theft, motor vehicle theft, and arson. These are Part I crimes and are serious crimes by nature and/or volume. Not all crimes, such as embezzlement, are readily brought to the attention of the police. Also, some serious crimes, such as kidnapping, occur infrequently. Therefore, the UCR Program limits the reporting of offenses known to the eight selected crime classifications because they are the crimes most likely to be reported and most likely to occur with sufficient frequency to provide an adequate basis for comparison. Part II crimes are all other offenses such as vandalism, alcohol violations, drug violations, loitering, etc.
For UCR purposes, Part I crimes are ranked in the order listed above with few exceptions. If more than one type of Part I crime occurs within the same event, only the crime with the highest ranking will be counted for statistical purposes. This hierarchy rule does not affect the number of charges for which a defendant may be charged with, or prosecuted for in the courts.
For more information on the Uniform Crime Reporting system visit the FBI's website at http://www.fbi.gov/ucr/