prisoner may seek relief under § 2254 “only on the ground that he is in custody in violation of the Constitution or laws or treaties of the United States.” 28 U.S.C. § 2254(a); see Del Vecchio v. Illinois Dep’t of Corr., 31 F.3d 1363, 1379 (7th Cir.1994). In the present context, that raises the question whether the corroboration rule discussed in Smith, Opper, and Wong Sun is constitutionally mandated. At least one circuit has held that it is not. See United States v. Dickerson, 163 F.3d 639 (D.C.Cir.1999) (characterizing corroboration requirement as a judicially created evidentiary rule); see also Lucas v. Johnson, 132 F.3d 1069, 1078 (5th Cir.1998) (Texas corpus delicti requirement is not constitutionally mandated); but cf. Aschmeller v. South Dakota, 534 F.2d 830, 831 (8th Cir.1976) (<HOLDING>). But we need not decide that question here
holding that trial court erred by not allowing the plaintiff to introduce evidence of prior dealings with the defendant holding that trial court did not abuse its discretion by allowing the state to introduce direct evidence of the controlling nature of defendants relationship with the victim holding that the district court erred in requiring the defense to disclose a report which the defense did not intend to introduce into evidence and which was merely designed to aid in the crossexamination of a witness for the state holding that even if the plaintiff had produced evidence of pretext  the evidence did not tend to establish a discriminatory purpose holding that state is required to introduce substantial independent evidence which would tend to establish the trustworthiness of the confession in conformance with opper