"reasonably suspected" could actually be rather arbitrary and capricious in practice.
I think the existing list is complete enough.
https://www.fbi.gov/about-us/cjis/nics/general-information/fact-sheet
A person who has been convicted in any court of a crime punishable by imprisonment for a term exceeding one year or any state offense classified by the state as a misdemeanor and is punishable by a term of imprisonment of more than two years.
Persons who are fugitives of justice—for example, the subject of an active felony or misdemeanor warrant.
An unlawful user and/or an addict of any controlled substance; for example, a person convicted for the use or possession of a controlled substance within the past year; or a person with multiple arrests for the use or possession of a controlled substance within the past five years with the most recent arrest occurring within the past year; or a person found through a drug test to use a controlled substance unlawfully, provided the test was administered within the past year.
A person adjudicated mental defective or involuntarily committed to a mental institution or incompetent to handle own affairs, including dispositions to criminal charges of found not guilty by reason of insanity or found incompetent to stand trial.
A person who, being an alien, is illegally or unlawfully in the United States.
A person who, being an alien except as provided in subsection (y) (2), has been admitted to the United States under a non-immigrant visa.
A person dishonorably discharged from the United States Armed Forces.
A person who has renounced his/her United States citizenship.
The subject of a protective order issued after a hearing in which the respondent had notice that restrains them from harassing, stalking, or threatening an intimate partner or child of such partner. This does not include ex parte orders.
A person convicted in any court of a misdemeanor crime which includes the use or attempted use of physical force or threatened use of a deadly weapon and the defendant was the spouse, former spouse, parent, guardian of the victim, by a person with whom the victim shares a child in common, by a person who is cohabiting with or has cohabited in the past with the victim as a spouse, parent, guardian or similar situation to a spouse, parent or guardian of the victim.
A person who is under indictment or information for a crime punishable by imprisonment for a term exceeding one year.
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