Greg Mitchell, boyfriend of Helena Stoeckley at the time of the murders in a signed, sworn statement said he could not remember being in Stoeckley's company on the evening of February 16-17, 1970. He had discussed the MacDonald murders with Stoeckley and that she claimed she was with Kathy Smith on the evening in question; that she did not take part in the murders and did not know who was involved. Mitchell also said he did not take part in the murders nor does he know who committed the murders.
On May 27, 1971, Mitchell agreed to and was given a polygraph examination by Robert Brisentine. (CID) The results concluded that Mitchell was truthful when he denied involvement in the murders of Colette, Kimberley and Kristen MacDonald. It was further concluded that Mitchell was truthful when he denied knowing the identity of the perpetrator(s) of the murders.