Authorities in at least eight states have checked for links between unsolved crimes and the suspects in the sniper shootings — a daunting task that has already led Louisiana and Alabama officials to file charges in recent local shootings.
State and local police have checked crimes from shootings to stabbings to see if ballistics or other evidence can link them to John Muhammad and John Lee Malvo, who had already been charged with 10 killings in Washington, D.C., Maryland and Virginia.
Spurred by a national advisory from the Maryland-based sniper task force, police have reopened old files to check for elements common with the sniper case.
Officials in Baton Rouge, La., said Thursday that ballistic tests had linked the two to the Sept. 23 murder of a beauty shop worker. Last week, Muhammad and Malvo were charged in a Sept. 21 slaying in Montgomery, Ala.
In Washington state, authorities say Muhammad and Malvo are suspected in a fatal shooting of a woman at her door in Tacoma in February, and a shooting that hurt no one at a Tacoma synagogue in May.
Attorney General John Ashcroft said Thursday that investigators were still exploring if other people helped Muhammad and Malvo.
Investigating what other crimes the men may have been involved in could be difficult because they have lived in or drifted through many states and spent time in the Caribbean.
Police have reported checks for any related cases in Washington, Oregon, California, Arizona, Louisiana, Alabama, Tennessee and Michigan.
Police in Baton Rouge, where Muhammad grew up, are seeking DNA samples from each man to check for any links to the serial murders of three women between fall 2001 and last summer. One woman was strangled, one stabbed and one had a slit throat.
However, authorities say they still suspect the killer was a white man. Muhammad and Malvo are black.
In Michigan, Lansing police were following up with the District of Columbia-area sniper task force looking for any connection to the shooting death of Bernita White at a zoo entrance in June 2001. She was shot by someone hiding behind a fence about 200 yards away.
It was unknown whether Muhammad and Malvo were ever in Michigan. But a friend of Muhammad's, who helped buy the car allegedly used in the sniper killings, was arrested in Michigan as a material witness.
At the sniper command center in Montgomery County, Md., detectives asked police agencies around the country to scan for similar cases soon after the sniper arrests.
"You just kind of look at everything to check if it really fits," said Brooks Wilkins, who oversees criminal intelligence for the Tennessee Bureau of Investigation.
Knowing Muhammad lived in Monterey, Calif., for about a year while in the military, the county sheriff's department scanned for any likely matches with all unsolved murders during that time. It came up empty, Deputy Bill Cassara said.
In Oregon, where Muhammad once served in the national guard, state police glanced back at several dozen sniping cases over the last decade or so, without finding any matches, spokesman Andy Olsen said.
N.G. Berrill, who teaches about criminal behavior at John Jay College in New York City, said investigators should look into every place the men went.
"There's every opportunity and every possibility that if he ran out of money, there would have been a robbery. If he had become angry or disconsolate or highly agitated, he might have shot someone," Berrill said.
"You would look at unsolved crimes that you had an itch to solve. I wouldn't confine it to a certain type of crime," added Jeffrey Smalldon, a forensic psychologist in Columbus, Ohio, who worked on the serial sniper case of Thomas Lee Dillon, who pleaded guilty in 1993 to killing five strangers.
Clint Van Zandt, a former FBI agent who examined patterns of criminal behavior, suggested police narrow their search. "I think part of what they need to look for is unsolved assaults or homicides where it appears the victim was again chosen at random," he said.
Northeastern University criminologist Jack Levin, who writes about serial murders, cautioned against scanning too aggressively for connections, because police could waste time and resources and finger the wrong suspect.
"When you've got guys like Muhammad and Malvo who are charged with crimes in a number of jurisdictions, there's a tendency for police departments around the country to want to clear their cases. Sometimes they go overboard," he said.
About 40 percent of all murders go unsolved.