Thank you for posting your question to History Hub!
We located the following entry in Find a Grave for John Weidler Cooper that appears to be a match to your father. We suggest that you visit your local library for assistance in viewing historical newspapers as libraries often provide free access to archived news websites to their patrons. You may want to search all Moberly, Missouri newspapers using the date May 18, 1978 or later as that appears to be the day after your father’s death date, which is listed as May 17, 1978. It is very likely an apartment fire would have been reported in local news publications.
It also appears your father served in the U.S. Navy. While his military record will not have any details regarding his death, you might be interested in requesting his personnel record from the National Personnel Records Center in St. Louis, Missouri. You can visit eVetRecs to submit a request online. You will need to provide proof of death, but the Find A Grave link posted above will suffice.
