A tarot card bearing a taunting message was found near the scene of one of the sniper attacks that have terrorized the Washington, D.C., area. As police try to determine whether the card is a message from the killer, or merely a prank, they may be thinking of past serial killers who have jeered at police — often in clues that led to their eventual capture.
Here is a look at some of the cases:
The Unabomber: Over the course of 18 years, Theodore Kaczynski carried out bombings that left three people dead and 29 injured. Investigators dubbed the killer the Unabomber because the original targets were associated with universities and airlines. He was caught when he released the ultimate taunt — a 35,000-word "manifesto," which he demanded newspapers print. When they did, his brother recognized his writing style and turned him in. Kaczynski was sentenced in 1998 to four life terms.
Son of Sam: David Berkowitz was caught in 1977 after a yearlong crime spree in New York during which he killed six people and wounded seven. A note he left at a crime scene read, in part: "I am a monster. I am the 'Son of Sam.'" Berkowitz sent several more notes, one to a reporter. Putting together the clues, the police eventually caught him. He is now serving a 364-year prison sentence.
The Zodiac Killer 1: There have been two Zodiac Killers. The first was confirmed to have killed five young people in the San Francisco area in the 1960s and 1970s, but he claimed a total of 37 victims. He was never caught, even though he sent a total of 21 letters to local newspapers, revealing details about the murders only the killer could know, enclosing in some envelopes swatches of cloth snipped from one of his victims, and signing off "Zodiac."
The Zodiac Killer 2: The second Zodiac killer attacked New York in 1990, shooting four people with different astrological signs, killing one. He wrote several notes to local newspapers and vowed to kill one person born under each of the 12 signs. Heriberto "Eddie" Seda was caught in 1996 and sentenced to at least 83 years in prison.
Hillside Strangler: This name, coined by the media, was actually two cousins who abducted, raped and killed 10 young women in the Los Angeles area in the late 1970s. The attackers taunted police by leaving their victims on hillsides, in areas where they were sure to be found — often near police stations. Angelo Buono and Kenneth Bianchi were eventually caught.
Jack the Ripper: The killer in one of the world's oldest and most notorious unsolved mysteries also taunted police through letters. Shortly after the second of the five murders he would commit between August and November 1888 in London, he identified himself as "Jack the Ripper." A subsequent letter included part of a kidney that he said came from one of his victims. In that letter he wrote, "Catch me when you can."
ABCNEWS' Andrew Chang contributed to this report.