An unknown man shot 56-year-old Ognjanovic on the street in the area of New Belgrade around 7:30 p.m. local time (5:30 p.m. GMT), according to police.
The lawyer died from his wounds at the scene while his son, who was also injured in the shooting, was taken to the hospital. Police inspectors and criminologists continue to work at the scene.
"The Ministry of Internal Affairs together with the prosecutor's office are taking all necessary measures to solve the case as soon as possible and to find the criminal," head of the criminal police department Dejan Kovacevic stated.
The confrontation between the Bojovic and Saranovic clans has led to several murders over the last five years.
Ognjanovic became famous after defending former Serbian leader Slobodan Milosevic at the Yugoslav war crimes tribunal against charges relating to the Balkan wars of the 1990s.
Milosevic was found dead in his cell at The Hague Tribunal's prison, reportedly due to a heart attack on March 11, 2006, while on trial for war crimes by the International Tribunal for the Former Yugoslavia.