Baton Rouge, La. ? Authorities charged the Washington-area sniper suspects with murder Thursday in a Louisiana attack and said they had definitively linked the two men to an Alabama slaying just two days earlier.

John Allen Muhammad, 41, and John Lee Malvo, 17, are now charged with a monthlong series of killings stretching from the Gulf Coast to the suburbs of the nation’s capital. Police nationwide are said to be looking for links to the men with help from federal authorities.

The two suspects face multiple state and federal counts in the Alabama and Louisiana cases and the sniper spree that left 10 people dead and three others wounded in Maryland, Virginia and Washington, D.C. They are also suspects in a February killing in Washington state.

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 Sept. 23 slaying and robbery of a beauty shop worker in the Louisiana capital.

Hong Im Ballenger, 45, died from a single shot to the head as she left work. Witnesses said the gunman was a young black man who fled into a nearby park and evaded bloodhounds called in to track him.

According to the arrest warrant, police believe Muhammad shot the woman and Malvo stole her purse and fled.

Earlier in the day, Alabama authorities said the same rifle, a .223-caliber Bushmaster, had been linked to the shooting death of a liquor store worker in Montgomery on Sept. 21, two days before the Louisiana slaying and 315 miles away.

In that case, the suspect allegedly Malvo was seen rifling through one of the victim’s purses before he was chased off by a police officer.

Hong Im Ballenger is shown in a family photo from 1997. Ballistics tests have matched the rifle used in the Washington-area sniper killings with the fatal Sept. 23 shooting of Ballenger, a Baton Rouge, La., beauty shop worker, police said Thursday.

The sniper suspects have been in custody in Maryland since they were captured at a highway rest stop Oct. 24. Authorities found the rifle in their car, which they say was modified so someone could fire unseen through a hole in the trunk.

In Washington, Atty. Gen. John Ashcroft said the investigation was continuing into the possibility other people may be involved or that the suspects have committed more crimes.

“We will proceed deliberatively, cautiously and not jump to any conclusions,” Ashcroft said. “The facts … will determine the final outcome and we intend to follow the facts wherever they may lead.”

A senior Justice Department official, speaking on condition of anonymity, said there was no specific evidence that others were involved but authorities would not rule out the possibility.

Police nationwide are checking unsolved crimes for links to the sniper suspects, the official said, with a particular focus on the Gulf Coast and East Coast.

In Alabama, officials said new ballistics evidence had linked the rifle to Claudine Parker, 52, who was shot to death during an attack that also wounded her liquor store co-worker, Kellie Adams, 24.

State forensics director Taylor Noggle said the slug taken from Parker’s body matched bullets test fired from the Bushmaster. Muhammad and Malvo have already been charged with capital murder in the crime.

First-degree murder carries a possible death penalty in Louisiana. Doug Moreau, the Baton Rouge district attorney, said he did not know when he would get the case and did not know whether he would push for the death penalty.

Englade said the unusual type of bullet used to kill Ballenger led police to investigate a possible connection. Police also said dated receipts from two Baton Rouge stores were found in the suspects’ car.

Muhammad grew up in Baton Rouge and still has relatives and friends there.

Also Thursday, officials in Prince Georges County, Md., where a 13-year-old boy was wounded outside his school, charged Muhammad and Malvo with attempted murder and conspiracy to commit murder, both of which carry life sentences.