IG does have the power to make arrests, get warrants, etc.:

§ 6. Authority of Inspector General; information and assistance from Federal agencies; unreasonable refusal; office space and equipment

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(e)

(1) In addition to the authority otherwise provided by this Act, each Inspector General, any Assistant Inspector General for Investigations under such an Inspector General, and any special agent supervised by such an Assistant Inspector General may be authorized by the Attorney General to—

(A) carry a firearm while engaged in official duties as authorized under this Act or other statute, or as expressly authorized by the Attorney General;

(B) make an arrest without a warrant while engaged in official duties as authorized under this Act or other statute, or as expressly authorized by the Attorney General, for any offense against the United States committed in the presence of such Inspector General, Assistant Inspector General, or agent, or for any felony cognizable under the laws of the United States if such Inspector General, Assistant Inspector General, or agent has reasonable grounds to believe that the person to be arrested has committed or is committing such felony; and

(C) seek and execute warrants for arrest, search of a premises, or seizure of evidence issued under the authority of the United States upon probable cause to believe that a violation has been committed.