The perp walk is a common custom of American law enforcement, the practice of taking an arrested suspect through a public place at some point after the arrest, creating an opportunity for the media to take pictures.
In 2011, the image of Dominique Strauss-Kahn being led by handcuffs by a team of law enforcement officers added to the international firestorm of how questionable the practice is. At the time, New York Mayor Michael Bloomberg did not mince words: “If you don’t want to do the perp walk, don’t do the crime”.
Many would say that law enforcement agencies use perp walks for their own PR. For the officers, there is the prestige of escorting newsworthy (alleged) perpetrators. The most infamous perp walk was of Lee Harvey Oswald in Dallas. He was shot by Jack Ruby as he was being perp walked through a parking garage.
http://en.wikipedia.org/wiki/Perp_walk
http://www.npr.org/2011/07/07/137681216/perp-walk-the-history-of-parading-suspects
photo source: