United States Court of Appeals For the Seventh Circuit ____________________ No. 20-2076 JUSTIN HERRERA, Plaintiff-Appellee, v. TERESA CLEVELAND, SAMUEL DIAZ, and ENRIQUE MARTINEZ, Defendants-Appellants. ____________________

Appeal from the United States District Court for the Northern District of Illinois, Eastern Division. No. 18-CV-6846 — Thomas M. Durkin, Judge. ____________________

ARGUED DECEMBER 1, 2020 — DECIDED AUGUST 6, 2021 ____________________

Before SYKES, Chief Judge, and BRENNAN and SCUDDER, Circuit Judges. BRENNAN, Circuit Judge. Justin Herrera, an Illinois state prisoner, filed a 42 U.S.C. § 1983 action against three correc- tional officers of the Cook County Jail for failing to protect him from assault and denying him prompt medical care. In his timely filed original complaint, Herrera named each of the defendants “John Doe” as a nominal placeholder until he 2 No. 20-2076 could ascertain the proper identities of the officers. Herrera then twice amended his complaint to include their actual names—but did so outside of the two-year limitations period. The officers moved to dismiss Herrera’s claim as time barred, and the district court denied that motion. Reasoning that suing “John Doe” defendants constituted a “mistake” un- der Federal Rule of Civil Procedure 15(c)(1)(C)(ii), the district court concluded that Herrera’s amended complaint “related back” to his original complaint. The officers then filed this in- terlocutory appeal. Because knowingly suing a John Doe de- fendant is not a “mistake” within the meaning of Rule 15(c), we reverse the district court’s judgment. I On October 25, 2016, Herrera—then a pretrial detainee at the Cook County Jail in Chicago—was physically assaulted by a group of detainees while temporarily placed together in a holding cell. 1 A fellow detainee accosted Herrera, accused him of affiliation with a rival gang, and threatened him. As the situation intensified, Herrera alerted the correctional of- ficers by banging on the door and calling for help. A correc- tional officer approached the cell to observe the situation, brushed off Herrera’s warnings, and walked away. Shortly af- ter, the aggressive detainee and eight others attacked Herrera, severely injuring him. Only after the assault did a correctional officer open the door and remove Herrera from the holding cell. Herrera then waited two hours before correctional

1 We gather these facts from Herrera’s second amended complaint filed on December 10, 2019. No. 20-2076 3 officers took him to the jail’s health service facility and an ad- ditional six hours before they transported him to a hospital. On October 9, 2018, seventeen days before the limitations period was set to expire, 2 Herrera filed a pro se complaint against three correctional officers assigned to monitor the holding cell on the day of his assault. He claimed the officers deliberately ignored his calls for help and denied him prompt medical care, in violation of the Fourteenth Amendment’s Due Process Clause. Not knowing the proper identities of the officers, Herrera named each of the three defendants “John Doe” as a nominal placeholder. Two months later, the district court published an order, adding Cook County Sheriff Thomas Dart as a nominal defendant and directing the U.S. Marshal to serve Dart. In that order, the district court denied Herrera’s motion for attorney representation and urged him to “identify and name the real parties in interest as soon as possible in order to avoid potential statute of limitations prob- lems.” After Dar