A parking ticket tripped up the Son of Sam, the Long Island sniper was found because of a burglary, and Oklahoma City bomber Timothy McVeigh drove too fast on his way out of town.
In mass-murder history, it's often the killers' own mistakes that are their undoing.
Washington-area police are hoping the same kind of break will lead them to whoever is responsible for a rash of sniper shootings that has killed seven people and injured two since Oct. 2.
Whether a killer takes out one person or many people over time, crucial mistakes usually are made, said Tod Burke, associate professor of criminal justice at Radford University.
Take David Berkowitz, the self-described Son of Sam who terrorized New York City for more than a year in the mid-1970s, killing six people and wounding seven with a .44-caliber revolver.
His mistake was parking illegally -- and getting a $25 ticket that led to his arrest.
"Here's this guy that was taunting the police with letters and everything else and how does he get picked up? Through a parking violation," Burke said.
A Brooklyn woman walking her dog on the night one of Berkowitz's victims was killed said she saw a car in front of a fire hydrant being ticketed and the owner carrying something in his outstretched right hand. She heard four gunshots, one right after the other, as she raced home in fear.
She did not notify police about what she had observed for several days.
When she did, police began tracing all cars given summonses in the area of the murder, and came up with Berkowitz's name. Berkowitz is serving six consecutive 25-years-to-life sentences and was denied parole earlier this year.
Mike Rustigan, a San Francisco State University criminologist, said serial killers eventually make mistakes because they start to feel invincible the longer they get away with their crimes.
"They really come to believe they're not going to get caught so they get overconfident," he said. "Then they'll make a mistake. It's kind of like pride goeth before the fall."
An example, Rustigan says, is Unabomber Ted Kaczynski, who went uncaptured during a series of mail-bomb attacks that killed three people and injured 23 between 1978 and 1995.
"The Unabomber would have been bombing into old age but his big mistake was in demanding that his manifesto be published" by The New York Times and The Washington Post, Rustigan said.
Police zeroed in after his brother, David, saw the 35,000-word treatise, suspected it was the work of his sibling and notified authorities. Kaczynski is serving a life sentence in federal prison in Colorado.
Driving too fast, without a license or in a stolen car has led to other high-profile captures.
After the bombing of the Murrah federal building in Oklahoma City, McVeigh was pulled over on an interstate highway north of the city for speeding in his yellow Mercury and driving without a license plate. Weapons charges, for the pistol strapped to his shoulder in a holster, were added later.
His connection to the bombing wasn't discovered until hours later when he was matched to a police sketch of "John Doe No. 1," the suspected bomber. McVeigh was executed last year.
The stolen car that serial killer Ted Bundy was driving led to his arrest. He confessed to more than 30 murders, including that of a 12-year-old girl, and was executed in Florida in 1989.
Mohammed A. Salameh's mistake was trying to get back his deposit for the rental truck that was loaded with explosives and destroyed in the 1993 bombing at New York's World Trade Center.
Salameh was arrested after he returned to the Ryder dealership in Jersey City, N.J., with police documents showing he had reported the vehicle stolen. Investigators had found vehicle fragments with an identification number matching the one on the van, and Salameh's involvement was confirmed after his rental papers tested positive for chemical nitrates, which is common to many explosives.
Asked why Salameh would have rented a truck in his own name, reported it stolen to police and the dealership and return twice seeking a refund of his $400 deposit, a senior law enforcement official at the time said: "Who knows? Just because he's a terrorist doesn't mean he's a brain surgeon."
In other cases:
-- Peter Sylvester, the Long Island sniper who shot and killed a man inside a diner and later wounded a woman inside a Burger King in 1994, ultimately was caught after police linked him to a burglary at a taxidermist's shop, where three guns had been stolen. One of the weapons, a .35-caliber rifle, turned out to be the murder weapon, which police found at Sylvester's mother's home.
--In a previous sniper case in the District of Columbia, police capped the investigation of an eight-week series of random shootings that killed four people after the suspect, James E. Swann, was caught running red lights. An off-duty police officer chased him into a parking lot, where he was arrested minutes after his final slaying.