Even an army of more than 1,000 law officers hunting for the Washington-area sniper cannot bring a promise of swift justice. It took 17 years to catch the Unabomber and longer to make an arrest in the Green River serial killings in the Northwest.
The 1996 Summer Olympics bombing suspect is still at large, and last year's deadly anthrax mailings remain unsolved.
Catching a serial killer can take years, or the hunt can just fade away into a smoke trail of false leads. Sniper killers are particularly hard to apprehend: they shoot from longer distances, often kill at random and generally leave few witnesses and little evidence.
"There are those who get away with murder," said Eric Hickey, professor of criminal psychology at California State University, Fresno.
The "Zodiac killer" who terrorized San Francisco in the late 1960s never was caught. An unknown sniper shot seven people, killing one, around New York City's Pennsylvania Station in 1983 and 1984, then disappeared.
Yet Hickey and others who study serial killers believe the Washington-area shooter or shooters will be found, and relatively soon.
They fear, however, it will come at the cost of more lives.
"You hate to say it, but every time he shoots someone, it brings you closer to him," said Hickey, who estimates about three-fourths of the U.S. cases attributed to serial killers have been closed.
"At the frequency he's doing it, he's going to get caught," Hickey said. "Unless he goes into hiding for a while."
Typical serial killer cases take months or years to close, but the pace of killing is slower than in Washington.
"Son of Sam" David Berkowitz killed six people and shot seven others in New York City over 13 months before he was caught in 1977.
The Washington-area sniper is blamed for killing nine people, and wounding two, within 13 days. The latest shooting was Monday night; since then the shooter has taken his longest break since his first attacks, on Oct. 2.
The killings became more personal for law enforcers when an FBI analyst was slain while leaving a Home Depot store in Falls Church, Va. Authorities do not believe her job was related to the killing.
Larry Thompson, the deputy attorney general, said more than 1,000 law officers "are doing everything we possibly can to identify the person who is responsible for these horrible and evil acts."
Those involved in the investigation include local police, Virginia and Maryland troopers, the FBI, the Bureau of Alcohol, Tobacco and Firearms, the Secret Service and U.S. Park Police. The Defense Department has promised help from military surveillance planes.
The FBI has assigned some 400 agents, including trainees taking tips called into a national hot line. That makes it one of the bureau's biggest cases, short of the war on terrorism.
A comparable FBI effort in a series of bombings at Atlanta's Olympic Park, a bar and two abortion clinics led to the indictment of Eric Robert Rudolph. He eluded a massive manhunt in the North Carolina mountains and remains on the 10 Most Wanted list.
The agency had better luck against the "railroad killer," Angel Maturino Resendiz, linked to 13 slayings across the country. He is on death row in Texas.
The Washington-area serial sniper seems to know the region well, allowing efficient escapes. Firing from afar with a high-powered weapon decreases the chance of leaving witnesses or physical evidence. The victims appear to be chosen at random.
But intense public attention on the case increases the chance someone will notice something suspicious that proves to be a vital tip.
At the same time, the shootings could stop as suddenly as they began with a spurt of six killings Oct. 2-3.
In Washington state and Oregon, 49 women, mostly prostitutes and runaways, were killed from 1982 to 1984. Then, apparently, the Green River killer quit killing.
Authorities said Gary Leon Ridgway, a Seattle housepainter, had been a Green River suspect since 1984. Advances in DNA technology led to his arrest last year in four of the slayings, and he awaits trial.
Criminologists say it is more likely the sniper would go on hiatus. Unabomber Theodore Kaczynski took a six-year respite before he resumed mailing deadly packages.
"They don't stop unless they are forced to stop," said Tod Burke, associate professor of criminal justice at Radford University in Virginia. "They may be in prison for another crime. Sometimes they die, or this person commits suicide and you never realize that was the spree killer."