S6·E22 Legend (1)

Episode recap

Role: Meticulous television and film archivist.
Task: Write a 280-380 word episode recap for NCIS S6E22 (Legend (1)).
Constraint 1: Write ONLY verifiable facts explicitly supported by the provided SYNOPSIS and SOURCES.
Constraint 2: Never invent/guess titles, names, dates, counts, awards, ratings, numbers, or plot points.
Constraint 3: If a detail is not in the material, omit it.
Constraint 4: Write original, neutral, encyclopedic prose in plain text.
Constraint 5: No markdown, no asterisks, no headings, no bullet points.
Constraint 6: Word count target: 280-380 words.
Synopsis: The body of a Marine leads Gibbs and McGee to the NCIS OSP division in Los Angeles, where a murder investigation quickly climbs to a matter of national security.
Sources:
[1] NCIS (2003) is a TV-14 Crime, Drama, and Action & Adventure series.
[2] Created by Donald P. Bellisario and Don McGill. Stars Sean Murray, David McCallum, Mark Harmon, Brian Dietzen. Follows the Major Case Response Team investigating cases connected to US Navy and Marines Corps personnel and families.
[3] Cast info (Season 1): Mark Harmon (Leroy Jethro Gibbs), Michael Weatherly (Tony DiNozzo), Sasha Alexander (Caitlin Todd).
[4] Title history: Navy NCIS -> Naval Criminal Investigative Service -> NCIS.
[5] Cast info: Mark Harmon (Leroy Jethro Gibbs), Sean Murray (Timothy McGee), Michael Weatherly (Tony DiNozzo/Anthony DiNozzo).
Episode: NCIS Season 6, Episode 22, titled Legend (1).
Plot: A Marine's body is found. This leads Gibbs and McGee to the NCIS OSP division in Los Angeles. The murder investigation becomes a matter of national security.
Characters involved in this episode (per synopsis): Gibbs, McGee.
Series context: NCIS follows the Major Case Response Team investigating criminal cases connected to the US Navy and Marines Corps personnel and their families.
The synopsis is extremely brief. It only mentions:
1. The body of a Marine.
2. Gibbs and McGee.
3. NCIS OSP division in Los Angeles.
4. Murder investigation.
5. Matter of national security.
The sources provide general series info:
1. Series title: NCIS.
2. Creators: Donald P. Bellisario, Don McGill.
3. Cast: Mark Harmon (Leroy Jethro