Crime in Milwaukee has decreased for an eighth consecutive quarter, according to statistics to be released Thursday by Milwaukee police, but Police Chief Edward A. Flynn cautioned that the downward trend could be slowed or reversed by the struggling economy and the early release of some prisoners.Crime in the city decreased 7.2% in 2009 when compared with the previous year and 11.9% when compared with 2007, according to the department's statistics.Violent crime - homicide, rape, robbery and aggravated assault - is down 12.8% when compared with 2008 and 20% when compared with 2007, the data shows.