The agency moved an application in the court of special CBI judge Mirza Zeenat seeking permission to conduct polygraph test on the former food and civil supplies minister with his consent.
The court has fixed June 13 as the next date of hearing on the application.
It has also issued notice to Raja Bhaiya asking him to present his case on the date of hearing.
They said although CBI does not have any evidence which directly links Raja Bhaiya with the murder of the DSP, it wants to get a clear picture of his role, if any, in the case.
The sources said findings of the test would not constitute evidence in the case, but it would give inputs which can be developed after thorough probe.
The agency has already grilled Raja Bhaiya on May 15 and 16 in connection with the murder case.
Haq's wife Parveen Azad had accused Raja Bhaiya of conspiracy after which he had to resign from the Cabinet on March 4.
