Murder accused Ambrose Monye gave the instruction to kill Chanelle Henning, the High Court in Pretoria heard on Tuesday.
Convicted murderer Willem Pieterse was asked why he killed Henning.
"It was an instruction we got from Ambrose," he answered.
The 26-year-old woman was shot dead while driving her car in Faerie Glen, Pretoria East, on 8 November 2011, shortly after dropping off her child at a creche.
Pieterse and Gerhardus du Plessis claimed Monye hired them to carry out the shooting and promised them R10 000 each.
Both accepted a plea bargain and were convicted in December last year of murder, possession of an unlicensed firearm, and possession of unlicensed ammunition.
They were each sentenced to 18 years in prison.
Pieterse was testifying in the murder trial of Monye and Andre Gouws.
Both have pleaded not guilty to murder, conspiracy to murder, conspiracy to procure an illegal firearm and ammunition, possession of an illegal firearm and illegal possession of ammunition.