After DiNozzo shoots the sniper, the FBI Agent is seen securing the weapon. Then DiNozzo checks the sniper's vehicle, talks to Gibbs and then in the background, the weapon can be seen being secured, again.
When Abby performs her "first autopsy" on the doll it is completely unnecessary. She cuts the doll head using an opening in the head several times larger than the slug. The slug would simply have fallen out when she set it on the tray.
Gibbs says that GYSGT Carlos Hathcock, a sniper, was credited with 39 kills. Gibbs apparently transposed the actual number of 93 kills. (Because of the difficulty in meeting the requirements, few kills were listed officially. Hathcock himself claimed more than 300.)
When Gibbs looks through the rifle scope to get a sight line on the recruiter's shooting his eye is almost touching the scope. These kinds of scope place the focal length (where your eyeball needs to be to see through the scope) several inches behind the frame of the scope to allow for clearance when the shot is fired. Otherwise the recoil would push the scope onto the shooter's eye.
The game being played at the start is Time Crisis II (1997), which does not feature commentary sounds like "you're under attack" and "bonus level".
When reenacting the scene of the sniper sighting recruiter Gunnery Sgt. Freddy Alvarez, the name tag on the recruiter's uniform shows "Allen", not "Alvarez". However, the reenacting of the first murder actually represents the initiation of the second one.
At the first sniper perch, Gibbs comments on the ability of the sniper to judge and remove precisely the one brick in the wall that will allow him to line up for a perfect kill shot. Sounds good, but removing just one brick will not provide enough clearance for both the muzzle of the rifle and a clear line of sight from the scope to the target. Both together on a typical 7.62mm sniper rifle are taller than the height of a common standard size red clay brick. At least two bricks from adjacent courses would need to be removed.
When Gibbs is on TV as the new recruiter a close up of the snipers eye is shown, it can clearly be seen the actor is wearing contact lens. In reality no marine sniper can wear contact lenses and must have unaided perfect vision.
At 26:25-crew members are visible in the TV screen.
The team finds a small feather and Gibbs makes a reference to GySgt. Carlos Hathcock, a Marine sniper in Vietnam. He says Hathcock had 39 confirmed kills, but this number was actually 93.
When showing the soldier his badge, Gibbs holds the NCIS card upside down.
In an earlier shows, Gibbs was a retired Marine MP. Makes sense. In this episode, he was a sniper. Much like JAG, the character being a lawyer (or MP) isn't cool enough.