Ton is a meassure of weight not counts.Nope. It is both. From dictionary.com "ton" entry:
"7. Informal a. A large extent, amount, or number. Often used in the plural: has a ton of work; gets tons of fan mail."
Also, please provide a reference.
Since you asked politely, here's one. Manhattan, which I don't consider an "inner city slum" had 88 homicides in 2005, 102 in 2006, 68 in 2007, 62 in 2008, etc.
That's comparable to Ireland, Switcherland, Denmark, Austria, countries of 3 to 6 times the population of Manhattan (1.6), and 3 to 4 times the percentage of murders in Germany (adjusted for the 80 million population).
http://projects.nytimes.com/crime/homicides/map