Yes, 28 CFR 600.3 which states that "(b) The Attorney General shall consult with the Assistant Attorney General for Administration to ensure an appropriate method of appointment, and to ensure that a Special Counsel undergoes an appropriate background investigation and a detailed review of ethics and conflicts of interest issues.
Also, remember that the Comey memo leak is what triggered the appointment of a special council. On May 16, the memo leaked. On May 17, a special council was appointed. So we are to believe that the selection of a council, a background investigation, and a detailed review of ethics and conflicts of interest was all done in one day and that they found no conflict of interest between Comey and Mueller when Comey is definitely a witness ( and now a potential target ) ? Now you know this must have been decided weeks prior, since they already had Mueller chosen and ready to go. This stinks of a setup.
If Comey was a witness he would not have been allowed to talk to in open session and prejudice the investigation.