A ghoul investigator (喰種捜査官, gūru sōsakan) is a specially trained professional employed by the Commission of Counter Ghoul. Most are stationed at the CCG Main Office in the 1st ward but many are occasionally granted authority of investigations in one of Tokyo's other wards. They are tasked with the investigation, pacification and elimination of ghouls to protect the civilians of Japan from any potential harm caused by ghouls. During their investigations, they analyze crime scenes for traces of ghoul perpetrators, expose their identities, incapacitate or neutralize them.
Ghouls refer to them as Doves (
Usually, ghoul investigators were instructed at and graduated from the CCG's Ghoul Investigator Training Academy. When they enter the CCG, they begin their career as Rank 2 investigators.
Rarely, ghoul investigators are employed even though they did not graduate from the Training Academy. These investigators are admitted by order of the CCG's chairman, Tsuneyoshi Washuu, and begin their career as a Rank 3 investigator. Known cases are Kishou Arima, Juuzou Suzuya, Haise Sasaki, Tooru Mutsuki, Saiko Yonebayashi, Ginshi Shirazu and Touma Higemaru.
New ghoul investigators are typically partnered with a senior investigator or join a squad to continue their training on the job.
Since the investigators as humans lack the physique, stamina, and strength to manually handle ghouls in combat, they are compelled to use tactical, man-made weapons. Only ghoul investigators are permitted to be armed with quinques, the most effective weapons against ghouls made from a ghoul's kakuhou. Additionally, they are sometimes armed with firearms loaded with Q bullets ammunition.
In compliance with the Ghoul Countermeasures Law, ghoul investigators must be constantly vigilant. After a crime scene has been found, ghoul investigators function like modern investigative law enforcement. Using the clues that remain at crime scenes, they are able to distinguish certain characteristics about their targeted ghoul. They analyze helpful clues, like footprints and clothing fibers, to more reliable ones, such as body fluids, hair, kagune secretions and kagune markings. The ghoul responsible will be referred to by either a number (e.g, "Number 696") or an alias (e.g, "Rabbit"), and contain their information in numbered files (e.g, 150919-27004). It will contain the targeted ghoul's habits, areas of predation, activity frequency, preferred victims, possible to confirmed relatives, as well as any previous run-ins and any capabilities and estimated strengths asserted afterwards.
Depending on the potential threat level of the ghoul, if the target is lower ranked, it can be pursued by a set of or a partnership including senior investigators, or a lower ranked squad, but should the ghoul be deemed as dangerous, only skilled high-ranked investigators are appropriate for continuation, either in a partnership or as a squad. Ghoul investigators may progress their search with interviews and meetings. Following the identification of possible suspects, they conduct surveillance until either their target's status as a ghoul is affirmed or proven false. During these investigations, ghoul investigators are sometimes backed up by the bureau investigators of the ward respective to the investigation.
If confirmed after the ghoul has fulfilled all requirements to be declared as such, the subject will be rated as per the ghoul rating outlines before exterminating it on scene or capturing the ghoul. Should the latter be the course of action they may send him/her to a ghoul detention center, either Corniculum or transferred to Cochlea until their disposal. If the investigator wishes to obtain a quinque from the ghoul, they must bide their time in battle until the ghoul unleashes their kagune to identify their Rc type, or location of their kakuhou. In addition, the CCG is the one and only organization in the world that conducts these investigations on ghoul-related cases.
Occasionally, ghoul investigators participate in large-scale operations. According to rank and skill, a commander is designated by the Chairman who in turn selects squad leaders. Investigators with partners will join one of these temporary squads (i.e, Squad 3, Owl Suppression Operation) while those in squads remain so (i.e, Quinx Squad, Tsukiyama Family Extermination Operation) unless they must combine with another at the operation Commander's request. They must continue to work in unison under the Commander's supervision until the operation's conclusion.
The CCG operates similar to a military or law enforcement agency, with a strict system of rank designating an investigator's abilities and authority. Rank determines an investigators' level of responsibility, access to high-risk missions and high-rated targets, salary rate, and numerous other aspects of their career. The ranks are divided into two separate categories, designating whether an investigator is considered a senior investigator or a junior still considered in training. While senior investigators may be partnered together as necessary, junior investigators cannot be partnered with other inexperienced investigators.
When in squads, the authority as squad leader is held by the one with the highest rank while the position of vice-squad leader goes to the member with the second highest.
- Special Class Investigator (特等捜査官, tokutō sōsakan): The highest possible rank, achieved by the smallest percentage of investigators. They are considered the strongest of all investigators, and typically command operations as well as oversee the daily running of their assigned wards.
- Associate Special Class Investigator (准特等捜査官, jun tokutō sōsakan): The second highest rank, achieved by a small percentage of investigators. They possess the authority to command operations or oversee individual wards as necessary.
- First Class Investigator (上等捜査官, jōtō sōsakan): The lowest rank to be considered a senior investigator, with most investigators achieving this rank later in their career. It is typical for an investigator to retire at this rank, and their responsibilities are typically training a junior partner. Very few investigators move beyond this rank, and reaching it before their thirties is considered the mark of an exceptional investigator.
- Rank 1 Investigator (一等捜査官, ittō sōsakan): The highest rank for a junior investigator, having gained experience but not yet at the peak of their career. On average, Rank 1 investigators are around twenty-seven years old when they are promoted.
- Rank 2 Investigator (二等捜査官, nitō sōsakan): This is the rank at which almost all ghoul investigators begin their career, after graduating from the Ghoul Investigator Training Academy.
- Rank 3 Investigator (三等捜査官, santō sōsakan): Bureau investigators begin their career at this rank. Ghoul investigators who begin their career at this rank are "special cases," made investigators without formal training at the Training Academy.