I believe the first reference is what makes this a Federsl Case at this point, but it was discussed previously quite extensively here. You can find that discussion in thread #3, around post# 650+ ( http://www.websleuths.com/forums/sh...Zhang-26-Urbana-9-June-2017-3-*Arrest*/page14 )
(1) kidnapping in which the victim is willfully transported in interstate or foreign commerce;.
if you read the official Conplaint document, they reference interstate or foreign commerce several times.
Further from the Justice Department
Conviction for the offense of kidnapping requires proof of transportation in interstate commerce, of an unconsenting person, who is held for ransom or reward or otherwise, where the accused's acts were knowingly and willfully committed. See United States v. Osborne, 68 F.3d 94 (5th Cir. 1995). See also United States v. Crosby, 713 F.2d 1066 (5th Cir.); cert. denied, 464 U.S. 1001 (1983). Proof is not required that the accused carried out the kidnapping for personal financial gain. See United States v. Childress, 26 F.3d 498 (4th Cir. 1994), cert. denied, ___U.S.___, 115 S. Ct. 1115 (1995). Situations falling within the "or otherwise" language of the statute have included those where the purpose of the kidnapping was to silence a potential witness, see United States v. Satterfield, 743 F.2d 827 (11th Cir. 1984), on remand, 599 F. Supp. 958, cert. denied, 471 U.S. 1117 (1985), and kidnapping for the purpose of sexual gratification, see United States v. McBryar, 553 F.2d 433 (5th Cir.), cert. denied, 434 U.S. 862 (1977). Section 2A4.1 of the United States Sentencing Commission's guidelines governs kidnapping offenses.
https://www.justice.gov/usam/criminal-resource-manual-1033-kidnapping-18-usc-1201-1202
If you look at United States v. McBryar - the victim was transported across state line. So, they must have evidence they crossed state lines or they plan to replace the federal charges with state charges and this was just a method to get him in custody.