David K. Feddersen challenges the sentence the district court 1 imposed after he entered a plea under North Carolina v. Alford, 400 U.S. 25, 37, 91 S.Ct. 160, 27 L.Ed.2d 162 (1970), to threatening to use anthrax to assault or kill federal employees, in violation of 18 U.S.C. § 115(a)(1)(B). At sentencing, the district court denied Feddersen an acceptance-of-responsibility reduction and sentenced him to 36 months imprisonment to be followed by one year supervised release.

On appeal, counsel has filed a brief under Anders v. California, 386 U.S. 738, 87 S.Ct. 1396, 18 L.Ed.2d 493 (1967), arguing that the district court erred in denying an acceptance-of-responsibility reduction, given that the shortcomings in Feddersen’s guilty plea “reasonably appeared to be a product of [his] mental illness.” After careful review of the record, we find that the district court did not clearly err in denying the acceptance-of-responsibility reduction. See United States v. Arellano, 291 F.3d 1032, 1034 (8th Cir. 2002) (standard of review).

*755 Upon reviewing the record independently under Penson v. Ohio, 488 U.S. 75, 109 S.Ct. 346, 102 L.Ed.2d 300 (1988), we have found no non-frivolous issues. Accordingly, we affirm. We also grant counsel’s motion to withdraw.