What is the story behind the mannequin in the window at 515 N. Washington St. in Alexandria? It has been there for as long as I can remember. The mannequin has remained throughout the years despite changes in the building’s usage and ownership. My father told me it was put there after a night watchman was killed when the building was a warehouse. It’s currently an apartment or condo called the Mill. Was my dad right?

Sarah Capponi, Fairfax, Va.

A file folder in the local history room of the Kate Waller Barrett Branch Library, just a few blocks away, contains much speculation about the figure gazing down from inside the handsome cupola atop the building at North Washington and Pendleton streets.

Apparently, he is called “Oscar.”

Before we get to him, let’s tour the building. It was built in 1847 as the home of the Mount Vernon Cotton Factory. During the Civil War, the building was appropriated by Union forces and used as a temporary holding facility for Confederate prisoners. After the war, it was again briefly a cotton mill and then the bottling plant of Robert Portner Brewing.

When the brewery closed, the building became the home of the Express Spark Plug factory. Photos from the 1920s show the exterior painted with such slogans as “The plug of continuous reliability” and “Be good to your motor.”

It seems to have been an office building briefly before being turned into the Belle Haven apartments in 1935. It’s back to being apartments after a stint as the headquarters of the International Association of Chiefs of Police.

In June 1933, a writer at the American Motorist magazine recounted the tales associated with the mannequin, which back then was not inside the cupola but in a window on the second floor. The most lurid story was that the dummy was connected to a slaying in the building.

In fact, there was a slaying. In 1854, a 24-year-old cotton factory night watchman named Michael Kiggin had his head bashed in.

The rumor was that the police dressed a mannequin in Kiggin’s clothes and put it in the window in an attempt to trick the killer into returning. There was an arrest in the killing, but the person accused was acquitted. Answer Man found no mention of the mannequin in 19th-century sources.

To check that story, the unnamed American Motorist writer visited 515 N. Washington. Spark plug factory workers told him the mannequin had been made by the Bureau of Fisheries and displayed around the country to promote angling. The oilskin garments on the dummy seemed to confirm the fishy provenance.

“Just when the figure was brought to the old Alexandria building, and why, was not known,” wrote the author. “But it was at least ten or twelve years ago.” That would date it to the early 1920s. (It’s possible the Fisheries Bureau had been a tenant and the dummy had been left behind.)

A factory worker said, “We used to keep it back here at the end of this room. It looked so natural and lifelike we would play practical jokes with it.”

In 1934, the mannequin was stolen by pranksters and found in the District, hanging from the Taft Bridge.

The author concluded: “Let it not be suspected that this article is an attempt to expose, debunk or destroy our neighborhood legend. Far from it. Good stories and mysteries are all too few in a world keen for detective problems and jigsaw puzzles.”

At some point, Oscar seems to have been removed from public view. A 2011 story in the Alexandria Times said he was reinstalled in the late 1970s after Bud Jordan, a real estate agent who had his office in the building, found it in storage and dressed it in an old suit.

The police chiefs association occupied the building from 1992 to 2014. For a few weeks in the late 1990s, Oscar was taken down so the cupola glass could be repaired, said Gene Voegtlin of the IACP.

“There was a nice little old lady who had lived her whole life in Alexandria,” Gene said. “She came to us and wanted to know why we had taken it out of the cupola. She said that when she had walked past it on her way to school, it scared her, but now that it was gone she missed it.”

The natural order was restored when Oscar went back.

In 2015, developer CAS Riegler started turning the building into the Mill. Brandon Lenk, of architectural firm Cooper Carry, was the project architect. Everyone involved was very aware of the mannequin, he said.

“The best way to put it is it was treated as though it was a historical aspect of the building,” he said. Contractors had to be careful not to damage it.

“It’s seen better days,” Brandon said of the mannequin. It’s missing a leg and is dressed in faded polyester. But how would you look if you were nearly 100 years old?

Twitter: @johnkelly

For previous columns, visit washingtonpost.com/john-kelly.