Prosecutors considered on Friday whether to file charges against a witness accused of intentionally derailing investigators by lying and claiming he saw a sniper open fire with an assault rifle, then later fleeing in a cream-colored van.
Fairfax County officials said the witness -- who was not immediately identified -- could be charged with filing a false statement.
"It would have been better if it didn't happen, but it didn't cripple the investigation," said Fairfax police Lt. Amy Luba. She said there were other witnesses to the shooting Monday.
The story began to unravel when police compared it to accounts from others who saw the shooting that killed an FBI cyberterrorism analyst in a crowded Virginia parking garage. Eleven people have been shot in the sniper attacks since Oct. 2, and nine have died.
Police said they don't have a composite sketch of the sniper who has terrorized Washington, Maryland and Virginia, leaving a tarot death card at one scene inscribed: "Dear Policeman, I am God."
Authorities say they haven't ruled out the possibility there could be multiple suspects.
Acting on tips and leads, police have served search warrants, checked motor vehicle records, searched military documents and used other tactics to sift through a constantly changing list of suspects.
Many people own guns that can fire the .223 caliber bullet used in the attacks, or drive white vans similar to vehicles seen leaving the shootings.
Police had several people under surveillance Monday night, according to a law enforcement source. They were cleared after the FBI agent was shot in a parking lot around 9 p.m.
That incident initially appeared to give police a big break in the case -- the first witness to actually see the sniper.
But Montgomery County Police Chief Charles Moose said Thursday the witness was not credible. He also chastised reporters for running reports about the weapon and descriptions of the suspect as olive-skinned, possibly Hispanic or Middle Eastern.
"We get this noise ... out there that gives people tunnel vision and makes them focus in on things that are not appropriate. ... We would like to be able to do our job."
Moose said the witness' emphatic description of the shooter's AK-74 assault rifle is also bogus. But investigators cautioned that they still believe the sniper is using one of a family of more than 30 similar assault-type weapons capable of firing a .223-caliber bullet.
"The message we're trying to say is please keep an open mind," Moose said. "People saw a description of a weapon over the last day and a half and we're convinced they eliminated people they know because they say, `Their gun is not the weapon I saw in the paper."'
Police have defended their tight control on information in the case, saying they don't potential witnesses to be influenced. They have, however, released composite drawings of white box trucks and vans that were reported leaving shooting incidents.
After two massive police dragnets failed to catch the killer, police increased their presence on highways. Virginia State Police spokeswoman Lucy Caldwell said troopers have doubled their patrols outside Washington by pulling in officers from other counties.
Investigators returned to the Home Depot parking garage in Falls Church on Thursday to make another sweep for possible evidence. At a parking lot across the street, police stopped all vehicles as they left and officers appeared to crouch down to search beneath them.
Schools in the region continued operating under lockdown restrictions, with outdoor sports and activities postponed. Montgomery County school officials planned a meeting next week to search for ways to salvage shortened fall sports seasons.
The Associated Press contributed to this report.