MILWAUKEE — One man saw the creature for only a few bone-chilling seconds, but he remembers that it was big, with heavy brown fur and a long tail, and not in any particular hurry as it walked through his neighborhood in Milwaukee and then disappeared into a thickly wooded ravine.

A police officer, tracking it the next day, described it as a “catlike animal” that had successfully evaded capture again. And Annie Nolen, a resident of the Brewers Hill neighborhood who spotted the animal slinking along a fence in her backyard, said she was momentarily paralyzed by the sight.

“I couldn’t move,” Ms. Nolen told local reporters later. “I thought, what am I looking at?”

Milwaukee officials are still not sure exactly what kind of animal has been spotted for the last week wandering through densely populated areas of this city, sitting under bridges, darting down hills and casually slinking past parked cars and small bungalows.

It could be a young African lion that was purchased on the open market, kept as a pet and then released when it became too large to handle, one wildlife expert speculated. (Wisconsin state law is notably relaxed on the possession of exotic animals.) Or it could be a cougar, an animal that has been spotted more frequently in populated areas of the Midwest in recent years. The Milwaukee County Zoo announced last week that all of its lions were safe and accounted for.