Penn professor Dr. Lawrence Sherman checked in from England by e-mail this morning to defend the idea of stop and frisk.

Sherman's work has been cited by both Michael Nutter and Chaka Fattah.

1. Gun detection patrols that include a "stop and frisk" based solely on evidence supporting reasonable suspicion of illegal gun carrying has been repeatedly upheld as constitutional in a series of US Supreme Court rulings over the past 40 years.

2. Well trained police officers using stop and frisk tactics in five independent tests in Kansas City, Indianapolis and Pittsburgh have substantially reduced gun violence. (See Dr. Ludwig's US Senate testimony at http://judiciary.senate.gov/testimony.cfm?id=754&wit_id=2066 ). These results have been peer-reviewed by either the US Department of Justice or the Brookings Institution.