After graduating from St. Louis University High School, Blassie entered the United States Air Force Academy, from which he graduated in 1970. He then attended Undergraduate Pilot Training, receiving his aeronautical rating as an Air Force pilot in 1971. He subsequently qualified as an A-37 Dragonfly pilot and served as a member of the 8th Special Operations Squadron, deployed to Southeast Asia. Blassie died when his A-37B Dragonfly was shot down near An Lộc in what was then South Vietnam.
Partial skeletal remains were retrieved from the area of the crash five months after his aircraft was shot down and were initially identified by Mortuary Affairs as Blassie. The remains were reclassified as unknown when their projected age and height were judged not to match Blassie's.
Blassie's remains were designated as the unknown service member from the Vietnam War by Medal of Honor recipient U.S. Marine Corps Sgt. Maj. Allan J. Kellogg Jr. during a ceremony at Pearl Harbor, Hawaii on May 17, 1984, and were transported aboard the USS Brewton to Naval Air Station Alameda. The remains were then sent to Travis Air Force Base on May 24, and arrived at Andrews Air Force Base the following day.
Many Vietnam veterans, President Ronald Reagan, and First Lady Nancy Reagan visited Blassie as he lay in state in the U.S. Capitol. An Army caisson carried his coffin from the Capitol to the Memorial Amphitheater at Arlington National Cemetery on Memorial Day, May 28, 1984. President Reagan presided over the funeral and presented the Medal of Honor to the Vietnam Unknown. The President also acted as next of kin by accepting the interment flag at the end of the ceremony.
DNA identification had yet to advance to its current state when Blassie's remains were repatriated, and he lay in the Tomb of the Unknowns up to 1998, with visitors paying respects but unaware of his identity.
A CBS News report in January 1998 claimed the Vietnam unknown was Blassie, and articles in U.S. Veteran Dispatch in 1994 and 1996 had made the same claim, drawing on Defense Department records.
After Blassie's family secured permission, the remains of Blassie were exhumed on May 14, 1998. Based on mitochondrial DNA testing, Department of Defense scientists were able to identify Blassie's remains. On June 30, 1998, the Defense Department announced that the Vietnam Unknown had been identified. On July 10, Blassie's remains were transported to his family in Saint Louis, Missouri, and were later reinterred at Jefferson Barracks National Cemetery. The Medal of Honor bestowed upon him as the Vietnam Unknown was not transferred to Blassie after his remains were identified.
Following the removal of Lt. Blassie's remains from the Tomb of the Unknowns, the marker at Arlington was replaced with one that read "Honoring and Keeping Faith with America's Missing Servicemen." Advances in technology, such as those that allowed the identification of Lt. Blassie, may lead to the eventual identification of all interments marked "unknown" from Vietnam.