The person of interest detained in connection with the murder of UnitedHealthcare CEO Brian Thompson has been revealed … and his name is Luigi Mangione.

Law enforcement sources tell TMZ … Mangione is being questioned by authorities in Altoona, Pennsylvania … though, he has not been charged in connection with the fatal shooting.

The New York Times first reported the person of interest had a written “manifesto” in his possession. Law enforcement sources tell TMZ … the manifesto is “critical of the healthcare industry.”

As TMZ previously reported, LM was detained by police after officials received a tip that a person of interest was seen at a McDonald’s. The search for the suspected shooter expanded nationwide after New York City Police Commissioner Jessica Tisch said the possible perp had fled NYC.

The Times reports the detained man showed police the same fake I.D. used to rent the hostel room in NYC, where the murder suspect is believed to have stayed prior to last week’s murder … and the detainee was reportedly in possession of a gun — possibly a “ghost gun” — and a silencer, according to law enforcement sources cited by the newspaper.