According to the Iowa Cold Case link above...
Three years after Strassburger went missing, a witness in a court proceeding in another state claimed to know about a homicide connected to Strassburgers case. Authorities described the information as extremely credible and said the witness knew information about Strassburgers disappearance that had never been publicly released. They were never able, however, to verify the witnesss account.
Investigators believe Strassburger was the victim of a homicide, but have never been able to prove it because Strassburgers body has never been recovered.
Given that info, we still cannot rule out Strassburger, however there was 9 years between the time Strassburger disappeared and Sand Canyon John Doe was found. Highly unlikely he could be the SCJD.
His mother passed away in 1998. Obit as follows:
DAVENPORT -- Jeanne E. Strassburger, of Davenport, died Monday, Sept. 21, 1998, at Genesis Medical Center-West Campus, Davenport. Services will be 10 a.m. Thursday at Runge Mortuary and Crematory, Davenport. Burial will be in Davenport Memorial Park. Visitation is 3-5 and 6-8 p.m. Wednesday at the mortuary. Mrs. Strassburger was employed for many years as a secretary at the Rock Island Arsenal before retiring in 1982. Jeanne was born Nov. 7, 1920, in Davenport. She married Louis L. Strassburger in June 1943. He died April 8, 1973. In lieu of flowers, memorials may be made to the American Cancer Society or a favorite charity. Survivors include a son, Gary Strassburger, Davenport; grandchildren, Chris and Julie Franklin, Davenport, Amie Nemitz, Davenport, and Kelly Strassburger, Charlotte, Iowa; great-grandsons, Joshua and Joey Nemitz; her mother, Viola McCannon, Wilton, Iowa; a sister, Patricia Whitley, of Nevada; and a brother, Tom McCannon, Wilton. She was preceded in death by a son, Dale Strassburger, in 1982, and a daughter, Nora "Beanie" Franklin, in 1988.
The is also an entry in Family History Library of a Dale W. Strassburger with the same birthdate related to a Sheila Strassburger (nee Spring). They lived in Bettendorf ,IA from 2001 thru 2004 and Moline IL from 1994 thru 2001. Not sure if there is a relation or not. Sheila is found in Largo Fl from Nov 2007-2009 and Clearwater FL from 2000-2004. Prior addresses are Macomb, IL from Dec 30, 2000 thru Dec 15, 2001, and Bettendorf , IA from Sept 1, 1983 thru Jan 2004. There is a marriage cert from San Diego in 1977 for a Sheila Spring to a Dale W. Strassburger. There is another Dale Allen Strassburger in Ca, but he was married to a Jill.