Advocate Andrea Johnson testify at the Madlanga Commission.

A string of key admissions by Investigating Directorate Against Corruption (IDAC) head Advocate Andrea Johnson dominated proceedings with her testimony exposing flaws in the process that led to the investigation of Crime Intelligence head Lieutenant General Dumisani Khumalo.

In her testimony at the Madlanga Commission on Wednesday, Johnson conceded that IDAC had no legal mandate to investigate Khumalo based on the information initially before it.

She also admitted that she incorrectly applied a subjective test rather than the objective "reasonable person" standard when assessing the Section 27 affidavit submitted by MP Fadiel Adams, describing the mistake as an honest error.

Johnson further acknowledged that IDAC was not authorised to solicit complaints from the public.