Fact sheet: What is known about the sniper
Twelve shots have been linked to the sniper. Nine people have been killed and two wounded. In the first shooting incident October 2, no one was hurt.
The shootings have yielded some consistencies.
The victims appear to be randomly selected as they go about life's routine tasks -- pumping gas, shopping, mowing the lawn.
The killer, who hasn't struck on weekends, may be driving a light-colored van or truck with a ladder rack on the roof. Police released composite pictures Tuesday of two white, mid-sized commercial trucks, a Ford Econoline and a Chevrolet Astro, seen near Friday's shooting in Fredericksburg, Virginia.
Investigators found a spent shell and a tarot card in a wooded area around the shooting at a Bowie, Maryland, middle school. The Tarot's "Death" card had a handwritten message on it: "Dear Policeman, I am God." (About Tarot cards)
The killer seems to favor suburban gas stations, killing four people as they pumped gas. Some station owners have aimed their surveillance cameras away from the pumps hoping to catch the sniper on film.
Shopping centers also appear to be favorite targets, having struck at four different malls.
The shooting spree began on October 2 outside a Michaels craft store in Aspen Hill, Maryland, but the bullet missed the intended victim.
Two days later, the sniper wounded a woman outside a Michaels in Fredericksburg, Virginia. The shooting October 14 happened outside a Home Depot that shares a shopping center with a Michaels store.
The shooter appears to choose victims near major thoroughfares, such as Interstate 95, that he can use to make a quick getaway.
The shooter is using a high-powered .223-caliber assault rifle or hunting rifle accurate up to 730 yards, police said. (Tracing bullets)
All of the deaths have been caused by a single shot -- "one shot, one victim," in sniper's parlance. Investigators have looked at the unique marks a gun's barrel leaves on shell casings to match them to a single shooter.
The reward for a tipster who helps catch the sniper is up to $500,000. Police established a tip line: 888-324-9800.
The latest victim was identified Tuesday as Linda Franklin, 47, an employee in the FBI's National Infrastructure Protection Center, which assesses threats against major structures and cyber networks. Franklin, who lived in Arlington, Virginia, was not assigned to the sniper case.
She was slain Monday night by a single bullet as she loaded packages into her car in the parking lot of a Home Depot store in northern Virginia.
Police were using witness accounts in the latest shooting to try to develop a sketch of the shooter.
How has sniper managed to elude capture?
Is more than one sniper involved?
What is the motive behind the killings?
Charles A. Moose: The Montgomery County police chief. Moose spent six years as the first black police chief in Portland, Oregon, before coming to Montgomery County. He holds a doctorate in urban studies from Portland State University. Montgomery County Executive Douglas M. Duncan hired Moose in 1999 for what he termed the chief's steady leadership skills.
Tom Manger: The Fairfax County police chief. He handled the investigation into the sniping shooting of a woman in the parking lot of a northern Virginia Home Depot.