In a series of conversations and flashback, Gibbs explained that his wife, Shannon Gibbs (Darby Stanchfield), was an unfortunate witness to a murder, committed by Pedro.
This prompted a vicious retaliation, forcing Pedro’s hand to protect himself by killing all witnesses – Shannon.
In a horrific set of scenes, Shannon and her daughter – Gibbs’ daughter – were killed in a car accident, as well as the NCIS agent who was assigned to their protection.
Gibbs was unable to assist at all, as he was abroad in combat, leaving him entirely helpless.