Christina Rojas was Samuel Gates, Jr.'s nanny.
Hired one year after Sam Jr.'s mother, Elizabeth, died of cancer, Christina and the boy developed a strong bond. After Sam was kidnapped, Christina was suspected of being an accomplice, as she had disappeared after the abduction and didn't answer her phone, but Gates didn't beleive Christina was involved because of her love for Sam.
In an effort to locate Sam, Reese visited Christina's apartment where he discovered she had been shot dead. Fusco later identified Drost as her killer using a nearby security camera and the description of one of the gang members given to him by Reese.