Category 2, Suspect knowledge
A. Involved in the same incidents as individuals in Category 1.
B. Lost in areas or under conditions that they may reasonably be expected
to be known by the enemy.
C. Connected with an incident that was discussed but not identified by name
in the enemy news media, or
D. Probably identified through analysis of all-source intelligence.

Category 3, Doubtful knowledge
This category contains individuals whose loss incident such that it is
doubtful that the enemy would have knowledge of the specific individuals.
(e.g., aircrews lost over water or remote areas.)

Category 4, Unknown Knowledge
A. Individuals whose time and place of incident are unknown (e.g., aircrews members downed at the unknown locations or ground personnel that were separated from their units at an unknown time or place), and
B. Who do not meet criteria of categories 1 through 3.

Category 5, Category unrelated to degree of enemy knowledge.
A. Individuals whose remains have been determined to be nonrecoverable as outlined in Department of the Army Technical Manual 10-286, January 1964, section 39.

Data from Defense Intelligence Agency --  20,  January 1982