Here is the full list of all 26 NCIS achievements worth 1,000 gamerscore. It takes around 4-5 hours to unlock all of the achievements on Xbox 360.
Successfully completed Episode 1
Successfully completed second crime scene
Successfully cracked first safe
Successfully completed first ballistics test
Successfully completed first autopsy
Successfully completed first interrogation
Successfully completed first satellite tracking
Successfully completed first deduction
Successfully completed first fingerprint comparison
Successfully completed first fingerprint lifting
Successfully completed first footprint comparison
Successfully completed first database search
Successfully completed first interview
Successfully completed first crime scene
Successfully completed first co-op activity
Collected first piece of evidence
Complete first chemical analysis
Complete Episode 2
Complete Episode 3
Complete Episode 4
Complete third crime scene
Complete fourth crime scene
Complete fifth crime scene
Complete sixth crime scene
Complete seventh crime scene
Save the world from terrorists