"I could not understand the attitude of casting away the future of their own people," Clive Derby-Lewis' wife, Gaye, testified.
She did not say who the so-called agents were acting for.
Asked whether her suspicions applied to all journalists opposing conservative views, she said: "To a certain degree, yes, that is my opinion."
Her husband, who was a Conservative Party MP, and Polish immigrant Janusz Walus were convited in 1993 of killing SA Communist Party leader Chris Hani outside his Boksburg home earlier that year.
Both were sentenced to death, but their sentences were commuted to life imprisonment when the death penalty was abolished.
They are seeking amnesty for the crime on the grounds that it was politically motivated.
Gaye was on Tuesday questioned about a list of 19 names which she compiled before Hani's assassination. Her husband gave the document, which contained Hani's name, to Walus shortly before the assassination.
The names of several journalists appeared on the list, including those of Tim du Plessis of Beeld, and former editors Ken Owen and Willem Wepener.
Gay said Du Plessis was "particularly vicious" against the CP.
Asked whether she had reason to believe he had also been bribed, she said: "Yes, from my point (of view) I could not understand his attitude."
She said she compiled the document with a view to writing articles about those listed. She then asked former Citizen reporter Arthur Kemp to provide her with their addresses.
President Nelson Mandela's name also appeared on the list.
George Bizos, acting for the Hani family, said: "Did you believe Mr Mandela would have given you an exclusive interview in his home?"
Gay: "Yes, why not? I am a journalsit."
She said she wanted to interview Owen because he had refused to publish the CP's point of view in the Sunday Times.
Asked if Owen had also been bribed, she said others had already named him as an agent.
The hearing at Vista University continues.