Can a plaintiff sue the City of Chicago for sexual assault?

Strauss v. City of Chicago, 760 F. 2d 765 (7th Cir. (Ill.), 1985), at pp. 767-8: Plaintiffs could file claims whenever a police officer abused them, add ... boilerplate allegations, and proceed to discovery in the hope of turning up some evidence to support the "claims" made. ... Proximate causation between the municipality's policy or custom and the plaintiff's injury must be present ... This emphasis on causality and on official policy supported our holding that the "allegation of a single incident of unconstitutional conduct by a municipal employee usually does not establish a sufficient basis for suing the municipality." ... A successful suit requires the plaintiff to establish that he was injured, and that some municipal policy, custom or practice proximately caused the injury.