Baton Rouge police Thursday said they have tied a once-unsolved murder to the serial snipers, reports CBS News Correspondent Bob McNamara.
The Bureau of Alcohol, Tobacco and Firearms confirmed that the same Bushmaster .223-caliber rifle was involved.
With the match, the same rifle has been tied to shootings in four states. Earlier Thursday, Alabama authorities said the weapon was linked to a September liquor store robbery and killing.
Meanwhile, a stolen handgun has been found near the scene of the Sept. 21 Alabama shooting that helped police zero in on the sniper suspects.
Police Chief John Wilson said the gun fits the make and model of a weapon believed used in the shooting outside a Montgomery liquor store that left one employee dead and another wounded.
Wilson said the gun, stolen July 20 at an El Paso, Texas, gun show, will be tested to determine if it is connected to the Alabama shooting.
John Allen Muhammad, 41, and John Lee Malvo, 17, face multiple state and federal charges for the shooting in Alabama and the series of sniper shootings in Maryland, Virginia and the District of Columbia that left 10 dead and 13 wounded.
Citing Justice Department officials, The Washington Post reported Friday that in the hours after his capture, Muhammad denied ownership of the car he was arrested in and the Bushmaster rifle inside it.
FBI agents and Montgomery County detectives questioned Muhammad at a secret location over a five-hour period Thursday, looking for information that would help prosecutors build their case against him and Malvo. But he would not answer any questions about the shootings, officials told the Post.
ABC News Thursday obtained a recording of a 911 call to Rockville, Md., city police on Oct. 15, in the midst of the Washington-area attacks, in which the caller claimed to be responsible for the murders.
"Good morning. Just listen. We're the people causing the killing in your area. Look on the tarot card. It says, 'Call me God.' Do not release the threats," the caller, believed to be Malvo, said.
"We have called you 3 times before, trying to cut off negotiations. We have gotten no response. People have died."
He was told by the police operator he would have to call the Montgomery County police department, because the city police were not investigating the shootings.
Louisiana officials said ballistic tests had linked Muhammad and Malvo to the Sept. 23 murder of a beauty shop worker — the second state to file murder charges after re-examining a local shooting for possible links to the Washington-area attacks.
Muhammad and Malvo were also tied to an Alabama murder two days before the Louisiana shooting.
Baton Rouge Police Chief Pat Englade issued first-degree murder warrants for Muhammad and Malvo after ballistics tests matched the rifle used in the sniper shootings to the shooting of Hong Im Ballenger, 45.
Ballenger died from a single shot to the head as she left the Beauty Depot. Witnesses said the gunman was a young black man who fled into a nearby park and evaded bloodhounds called in to track him down.
Muhammad, formerly known as John Allen Williams, grew up in Baton Rouge and still has relatives and friends there, including one of his ex-wives. He visited the area this summer, friends said.
"I would never have thought John would be involved in anything of this nature. He was just a beautiful person. He was a loveable person," his aunt, Yvonne Bradford-Williams, told CBS News.
Muhammad and Malvo have been in federal custody since their Oct. 24 arrest at a Maryland rest stop. Authorities recovered the Bushmaster rifle from the 1990 Chevrolet Caprice in which the two were found sleeping; that car had a hole in the trunk that could allow someone to fire shots undetected.
Attorney General John Ashcroft is considering whether the federal government will take the lead in prosecuting the two or have the first trials in Maryland, Virginia or elsewhere. Muhammad and possibly Malvo could face the death penalty if convicted on the charges filed so far.
Authorities have already laid charges in Alabama and linked two shooting cases in Washington state, all with ballistics evidence. In at least three other states, police have identified specific murder cases they believe could be linked — but with little real evidence so far.
The task has been daunting.
Muhammad and Malvo 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.
"It's difficult because he could reasonably be a suspect in just about anything," said Stanton Samenow, a psychologist who evaluates violent criminals for the courts and wrote "Inside the Criminal Mind."
Spurred by a national advisory from the Maryland-based sniper task force, police in many states have reopened old files to check for elements common with the sniper case. That three-week killing field left 10 dead and three wounded and brought charges from Virginia, Maryland and federal prosecutors.
N.G. Berrill, who teaches about criminal behavior at John Jay College in New York City, said investigators should try to reconstruct every place where the men went — especially Muhammad.
"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," he 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. Dillon pleaded guilty in 1993 to killing five strangers.
However, Clint Van Zandt, a former FBI agent who examined patterns of criminal behavior, suggested police could focus 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, in Boston, who writes on 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.