The dramatic drop in Baltimore City’s homicide rate has coincided with a sharp fall of another statistic: arrests.

Baltimore police are on track to make about 20,000 fewer arrests this year than in 2005, a 25 percent decline. Meanwhile the city’s homicide rate has fallen to the lowest level in three decades, raising questions about the benefit of the highly touted zero-tolerance policy that led to nearly 750,000 arrests between 1999 and 2006, but made little dent in the number of homicides.