THE HAGUE, Netherlands (AP) — A lawyer who represented a key witness in a major Dutch organized crime trial has been shot dead in Amsterdam, sparking calls for a tougher crackdown on violent underworld gangs.

Police said that 44-year-old lawyer Derk Wiersum was fatally shot Wednesday morning by a man who fled on foot.

Wiersum represented a witness identified only as Nabil B. in a criminal case against suspected underworld bosses accused of involvement in a string of killings. The witness was involved in one of the slayings but cut a deal with prosecutors to provide evidence in return for a lighter sentence.

Amsterdam Mayor Femke Halsema visited the scene of the slaying and called it "a shock for our society because the victim was doing his job."