They had the legal right to arrest the defendant in a public place once there was probable cause to believe he had committed a crime, even in the absence of an arrest warrant. See 18 U.S.C. § 3052 (authorizing FBI agents to “make arrests without warrant . . . 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.C. § 3061(a)(3) (identical authorization for USPIS Postal Inspectors); United States v. Watson, 423 U.S. 411, 423-24 (1976) (holding that warrantless probable cause arrests are constitutional); United States v. Shabazz, 533 Fed. Appx. 158, 162 (3d Cir. 2013) (“An arrest without a warrant is lawful if there is probable cause.”)