In Part I, the UCR indexes reported incidents of index crimes which are broken into two categories: violent and property crimes. Aggravated assault, forcible rape, murder, and robbery are classified as violent while arson, burglary, larceny-theft, and motor vehicle theft are classified as property crimes. These are reported via the document named Return A – Monthly Return of Offenses Known to the Police. Part 1 crimes are collectively known as Index crimes, this name is used because the crimes are considered quite serious, tend to be reported more reliably than others, and the reports are taken directly by the police and not a separate agency which aggregates the data and does not necessarily contribute to the UCR.