Brandie ATKINS, as administrator of the estate of William O. Atkins, deceased, Plaintiff-Appellant,
v.
CITY OF CHICAGO, et al., Defendants-Appellees.

*825 Joseph A. Longo, (argued), Attorney, Longo & Associates, Mt. Prospect, IL, for Plaintiff-Appellant.

Benna R. Solomon, Attorney, City of Chicago Law Department, Mary Ellen Welsh (argued), Attorney, Office of the Attorney General, Civil Appeals Division, Chicago, IL, Ruth F. Masters (argued), Attorney, Oak Park, IL, for Defendants-Appellees.

Before POSNER, MANION, and HAMILTON, Circuit Judges.

*826 POSNER, Circuit Judge.

This is the second appeal from the dismissal of a federal civil rights suit. 42 U.S.C. § 1983. The district court initially dismissed it under Rule 25(a)(1) of the Federal Rules of Civil Procedure, on the ground that the motion to substitute the plaintiff's widow for the (original) plaintiff who died while the suit was pending, was untimely. We reversed, 547 F.3d 869 (7th Cir.2008), instructing the district judge to allow the substitution. That kept the case alive, but the judge has again dismissed it, this time on the merits—he ruled that the complaint failed to state a claim. Hence this second appeal.

In October 2003 Chicago police stopped a car in which William O. Atkins, the plaintiff's decedent, was a passenger, and arrested him on the strength of a parole-violation warrant bearing the name "William Atkins." He was held at the police station overnight and then transferred to the custody of the Illinois Department of Corrections, which placed him in Stateville prison. From the moment of his arrest he steadfastly denied that he was the William Atkins named in the warrant, but alternatively and inconsistently claimed that he was indeed the same Atkins but that his parole had expired, so that he could not have violated it—which seems in fact to be the case.

Released from the Department's custody after 37 days when the parole board acknowledged that he was being detained in error, Atkins sued the arresting officers, who are employees of the City of Chicago, plus the City itself, prison guards at Stateville, and other employees of the Department of Corrections. The state defendants are accused of having unjustifiably protracted a mistaken detention and imposed impermissible hardships during it, all in violation of rights conferred by the due process clause of the Fourteenth Amendment. The charge against the City defendants is that the arrest was unconstitutional because it was not based on probable cause; and we'll start there.

When arrested, Atkins denied that he was the William Atkins named in the warrant and noted discrepancies between his identifying characteristics and the description in the warrant. Although both Atkinses were of the same race and sex and had the same first and last names, our William Atkins was slightly taller and somewhat heavier than the person described in the warrant and had a middle initial, which the name on the warrant lacked. But oddly—if they were different people—the month and day of their birth (though not the year) were the same and the first three digits of their social security numbers were also the same.

The police did not have probable cause to stop the vehicle in which our William Atkins was riding, but clearly if he was the William Atkins named in the warrant the illegality of the stop did not invalidate the arrest. United States v. Johnson, 383 F.3d 538, 544-45 (7th Cir.2004); United States v. Green, 111 F.3d 515, 521 (7th Cir. 1997); contra, United States v. Lopez, 443 F.3d 1280, 1285-86 (10th Cir. 2006). In Green we said the question was whether "the causal chain has been sufficiently attenuated to dissipate the taint of the illegal conduct," 111 F.3d at 521, and in like vein in Johnson we considered whether "a lawful arrest based on any outstanding warrant for a passenger in the vehi