The three accused were identified as Sanjeet Kataria, Deepak and Lalit, police said.
They were hired by the jailed gangster Ashok Rathi for contract killing of his own wife. The accused are friends of Rathi. Sushma was killed while she had gone to drop her daughter to school on September 2, they said.
According to police, the three accused hailed from Haryana and they met Rathi in the jail.
Rathi gave a contract to kill his wife as he suspected her character, they said.
Sushma received four bullet injuries and died on the spot.
A case was registered at Bhondsi police station in this regard.
Rathi had killed his mother-in-law and brother-in-law, some years ago and is serving life imprisonment for those killings.