United States marshals and their deputies may carry firearms and may make arrests without warrant for any offense against the United States committed in their presence, or for any felony cognizable under the laws of the United States if they have reasonable grounds to believe that the person to be arrested has committed or is committing such felony.
18 U.S. Code § 3053 - Powers of marshals and deputies
Minor changes were made in phraseology.
Functions of all other officers of Department of Justice and functions of all agencies and employees of such Department, with a few exceptions, transferred to Attorney General, with power vested in him to authorize their performance or performance of any of his functions by any of such officers, agencies, and employees, by Reorg. Plan No. 2 of 1950, §§ 1, 2, eff. May 24, 1950, 15 F.R. 3173, 64 Stat. 1261, set out in the Appendix to Title 5, Government Organization and Employees.