Plaintiff Felicia Morgan has long suffered from mental illness and has spent a large portion of her life incarcerated. While imprisoned, Morgan was temporarily moved to United Community Hospital (UCH), a private contractor that housed severely mentally ill inmates for Wayne County, Michigan. Three Wayne County deputies were scheduled to supervise the inmates in the UCH ward at all times. But on the afternoon of November 15, 2005, one deputy took his lunch break and a second left to use the restroom, leaving only one deputy in the unit. During those moments, there was a sexual encounter between Morgan and another inmate. After her release from prison, Morgan filed this lawsuit, alleging that the county and the on-duty deputies were deliberately indifferent to a serious risk of harm to her. The district court entered judgment in favor of defendants, and we affirm.

MURPHY, Circuit Judge. Federal law makes it a crime for so-called “straw purchasers” to tell licensed firearms dealers that they are buying a firearm for themselves when, in fact, they are buying it for someone else. 18 U.S.C. § 922(a)(6); Abramski v. United States, 573 U.S. 169, 179–89 (2014). Straw purchasers sometimes engage in these stealth transactions because the true buyers (for example, felons) cannot buy guns themselves. 18 U.S.C. § 922(g)(1). These types of straw purchases raise heightened safety concerns, so the Sentencing Guidelines instruct courts to increase a straw purchaser’s potential sentence in certain cases if the purchaser had “knowledge” or “reason to believe” that the true buyer could not lawfully possess the firearm. U.S.S.G. § 2K2.1(a)(4)(B).

What does it take for a straw purchaser to have “reason to believe” that the true buyer cannot lawfully possess the gun? This case raises that question. Dominique McKenzie admits that he was a straw purchaser for two individuals but disputes that he had “reason to believe” that they could not possess firearms. We interpret that phrase—one commonly used in the probable-cause context—to require, at most, that a straw purchaser know of facts creating a fair probability that the true buyer could not possess a firearm. And we agree with the district court that McKenzie had knowledge of such facts in this case. We thus affirm its use of this guideline.

SUTTON, Chief Judge. Marlon Portis and Demonte Thompson pleaded guilty to conspiring to rob electronics stores and to using firearms in the process. The plea agreements prohibited the defendants from bringing direct or collateral challenges to their convictions. Relying on a later U.S. Supreme Court decision that limited what offenses qualify as crimes of violence, United States v. Davis, 139 S. Ct. 2319, 2336 (2019), they filed these collateral challenges to their firearms convictions under § 2255, claiming that this change in law permits them to sidestep the plea agreements’ prohibitions on bringing collateral challenges to their convictions. Because they knowingly and voluntarily waived these challenges in their plea agreements and because later developments in the law do not permit the parties to the contract— whether the government or a criminal defendant—to back out of their obligations, see United States v. Bradley, 400 F.3d 459, 463 (6th Cir. 2005), we dismiss their appeals.