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In U.S. slang, the expression perp walk designates a march into or out of a police car, courthouse, etc., that a person in police custody is made to perform for the benefit of the news media.

This expression occurred, for example, in the following, by Joanna Weiss, published in the Boston Sunday Globe (Boston, Massachusetts, USA) of Sunday 22^nd May 2011 [page K9, column 1]:

No shame in imposing shame
Outcry against ‘perp walk’ is misplaced

So the French are up in arms about the “perp walk.” Dominique Strauss-Kahn, the rich and powerful head of the IMF, was handcuffed just like any other accused rapist in New York, paraded in front of the New York press: sans tie, sans dignity, sans key to his penthouse suite.
[…] French law bars the press from airing pictures of unconvicted people in handcuffs. […]
[…] But objections to the perp walk aren’t limited to the French. The practice has long been controversial in American legal circles—particularly after Rudy Giuliani, as a US attorney in the 1980s, started using the perp walk on white-collar defendants, subjecting powerful Wall Street types to common-criminal shame.
Defense attorneys argue, with some justification, that the image of a shackled defendant could taint a jury pool and impede a fair trial. […]
But as prosecutors argue, the perp walk can serve legal purposes, as well. It can be a deterrent (although it didn’t seem to clean up Wall Street). It can show that the government is serious about catching criminals. And it can send the clear message that no one is above the law—not even a brilliant, wealthy, politically connected man.

In the expression perp walk, the U.S. slang noun perp (a shortening of perpetrator first recorded in 1968) designates the perpetrator of a crime.

—Cf. also, in British-English slang, the verb frog-march (somebody), which means: to force (somebody) to walk forward by holding and pinning their arms from behind.

These are, in chronological order, the earliest occurrences of the expression perp walk that I have found:
—Two notes: 1) The first two texts contrast the professional methods employed by Rudolph Giuliani (born 1944), then U.S. Attorney for the Southern District of New York, with those employed by Charles Hynes (1935-2019), then Special State Prosecutor for the New York City Criminal Justice System. 2) In these texts, the use of “the now traditional “perp walk”” and of “what is called in the trade a “perp walk”” indicates that this expression was already well established:

1-: From New York Forum: About Crime: The Prosecutor As ‘Superstar’, by Richard Emery, staff attorney with the New York Civil Liberties Union, published in Newsday (New York City, New York, USA) of Tuesday 4^th November 1986 [page 54, column 1]:

Unlike any prosecutor in memory, Hynes declined all press statements, citing to the media the presumption of innocence of the men and women he was about to prosecute. No leaks can be traced to his office. […]
Even more amazing, when Hynes recently obtained indictments against corrections officials, he appropriately noted on his cryptic press release that an indictment is not evidence of guilt against the accused but merely a document that initiates a criminal proceeding. He has also refused to parade defendants before cameras in the now traditional “perp walk” that many prosecutors use to please the TV stations.

2-: From Prosecutor with a different style, by Nat Hentoff, Copley News Service, published in The Times (Hammond, Indiana, USA) of Tuesday 9^th December 1986 [page A-6, column 3]:

The presumption of innocence, rumored to be the cornerstone of our system of justice, is actually as hard to find as a manual typewriter.
Before trial, and sometimes even before an indictment, prosecutors orchestrate press conferences at which the defendant’s alleged crimes are so vividly detailed that he appears to already be on the way to the slammer.
[…]
Throughout the country, many prosecutors also put defendants through what is called in the trade a “perp walk.” The prosecutor, again before trial, alerts television stations when to bring in their cameras to get some “eyewitness shots” of the alleged malefactors. Under such circumstances, even Mother Teresa would look extremely suspicious, especially if her hands were cuffed behind her back.

3-: From Testing tensions between 1^st and 6^th Amendments, by Richard Sanger, News-Journal columnist, published in The Morning News (Wilmington, Delaware, USA) of Thursday 12^th November 1987 [page A15, columns 4 & 5]:

Somewhere I have read that parading a shackled defendant in front of the press is what is known as a “perp walk.” That’s “perp” as in “perpetrator.” The “perp walk” is what they call a “photo opportunity” in Washington—an event staged primarily for self-serving purposes, but billed as a favor to the press.
[…]
[…] The press unfailingly rises to the bait. When was the last time some prosecutor threw a perp walk and nobody came? Fact is, all kinds of people turn out for such an event, even as they did when lashes and other humiliations were imposed in the town square. Folks like Jack Ruby, for instance. It was, after all, a perp walk that was Lee Harvey Oswald’s last walk in Dallas.