Sterling worked as a technician in a forensics lab in Maryland that handled specialized work farmed out from the Baltimore Police Department's larger lab.
During his career as a Baltimore detective, DiNozzo accused a scientist at the lab, George Stewart of contaminating blood samples, resulting in the collapse of a case against a murder suspect.
In the end, Stewart was fired, and his wife divorced him, but he counter-sued the state, claiming that the real mistake had been made by Sterling's lab. Stewart won the court case, resulting in the lab being shut down and Sterling was fired from his position.
Planning revenge on both DiNozzo and Stewart, Sterling applied for a job at NCIS, and was assigned to Abby as her assistant by Jennifer Shepard who at the time was unaware of Sterling's past or his true intentions. This didn't go down well with Abby and Special Agent Leroy Jethro Gibbs, both of whom said that Abby worked best alone. Shepard ignored their pleas and asked them to give a month and then they would talk.
Abby did not take to "Chip," as she was quick to nickname him, over his protests.
Gradually, however, "Chip" established himself as a capable assistant. He helped her in the investigations of two Marine wives missing in connection with an Internet sex site, and also comforted DiNozzo after he received a savage beating, while undercover as a contract assassin.
A short time later, however, a woman's severed legs were found at Quantico and all of the forensic evidence identified Tony as the murderer, enough to (briefly) convince even Abby that her science was faulty.
But Abby, knowing that Tony wasn't guilty, kept digging, and the woman's legs were eventually traced to the body of a "Jane Doe" at a county morgue, where George Stewart (now under the alias Petri) was working as a coroner. Chip's scheme was actually a double-fix: he would implicate DiNozzo, and if the frame-up was discovered, it would eventually lead back to Stewart/Petri, who had also played a role in Chip getting fired.
Tony was eventually cleared of all charges, and Petri was arrested. Abby, however, was not satisfied, and kept digging, eventually discovering the connection between Petri and Chip's old lab. She started to telephone the lab to get a list of its old employees, when Chip cut off the line and menaced her with a knife.
At the same moment, up in the squadroom, Gibbs opened a sealed file from Petri's old lawsuit, and saw a photo of Chip in the witness box.
The team rushed downstairs to rescue Abby, but it turned out to be unnecessary. Abby indicated Chip, who had been neatly trussed up and gagged with duct tape, and reiterated her request to work alone.
Stewart was presumably arrested and tried for framing DiNozzo and Petri, and for attempting to kill Abby (though he had not actually murdered anyone).
It is unknown if "Charles Sterling" was his real name, or if this was just an alias he adopted when he applied to NCIS.
The episode of DiNozzo's frame-up was very trying for Gibbs; when, shortly thereafter, Timothy McGee unknowingly shot an undercover police detective, Gibbs began to rant that NCIS was under some kind of curse, wondering if someone had broken a mirror, leading to their bad luck. (Probie (episode))
It was likewise a trying affair for Abby; a short while later, when Gibbs told her, apparently seriously, that her new assistant would be starting soon, she broke down and began to plead, before realizing that Gibbs was joking. (Model Behavior (episode))
Chip was mentioned in the Season 6 episode, Murder 2.0 (episode) where Abby was left shaken after the serial killer responsible had slipped a camera into one of the janitor's lunchboxes and then begun broadcasting a live video feed which McGee later traced to being outside Abby's lab, suggesting that she was a possible target.
In the Season 8 episode, Worst Nightmare (episode), it was revealed that even six years after the whole Chip affair, Abby was still shaken over the incident as such, was unwilling to trust anyone assigned to her lab.
When his scheme was revealed, Chip gloated, with some justification, that his frame-up had actually been quite clever. After removing the Jane Doe's legs from the morgue, Chip artfully planted a set of trace evidence:
- DiNozzo's blood, off a tissue that he had used when he had a nosebleed at the end of Under Covers (episode) which Chip secretly palmed;
- Carpet fibers from DiNozzo's car, which Chip took when Abby ordered him to move DiNozzo's car;
- An apple that DiNozzo had taken a bite from, which Chip used to replicate the bite pattern on one of the legs;
- The fingertip of a glove that DiNozzo had worn on a previous case (thus leaving his fingerprint inside), which Chip left at the scene with the legs.
Furthermore, when the legs were eventually identified, through a bone marrow donor who was alive and well, they were traced back to a morgue at which Stewart/Petri worked, who would be the obvious suspect in framing DiNozzo.
Chip's one mistake was leaving his own piece of trace evidence: a gooey substance on one of the legs, which Abby determined was residue from a crime scene glove, which also had a minute amount of the real criminal's sweat on it. Abby was in the process of testing this residue for DNA when Chip confronted her.
Despite being soft-spoken, Chip was easily brushed aside by Abby, Gibbs, Tony and everyone else but he also displayed a sinister side.
He also had a long-standing grudge against Tony who he blamed for ruining his career and getting him fired.
But unlike other people who would get their revenge in public, Chip used his own forensics skills to frame Tony for murder while pretending to be the good guy, the innocent bystander and he would have successfully pulled it off had Abby not been so devoted to finding out who had framed Tony for the crime he'd supposedly committed.
- Chip was portrayed by Michael Bellisario, son of NCIS creator Donald Bellisario, and half-brother of actress Troian Bellisario, who played McGee's sister Sarah in the episodes Red Cell (episode), Family Secret (episode) and Twisted Sister (episode). Michael is also the stepbrother of Sean Murray who plays Timothy McGee on the show.