As investigators sort through conflicting witness statements about vans, trucks, facial characteristics and possible accomplices associated with the area's serial sniper, most have turned out to be too vague to publicize.

But Monday's attack netted a seemingly solid lead - a witness says he's sure that the gunman used an AK-74 assault rifle to kill 47-year-old Linda Franklin outside the Home Depot store in Falls Church, Va.

That observation, if true, raises more puzzling questions about the serial sniper and his methods. For instance, a gun expert familiar with the AK-74 - cousin to the better-known AK-47 - says the publicized details of the case don't jibe with the firing capabilities of the AK-74, a semiautomatic rifle that ejects a shell casing every time it is fired.

Only once, after a 13-year-old boy was shot Oct. 7 in Bowie, have police said they recovered a shell casing. Authorities said they found the shell casing in the woods near a tarot card. "Every time you pull the trigger, a cartridge goes flying. I'm talking about flying 8 or 10 feet," said Sanford Abrams, owner of Valley Gun in Parkville.

"Either he's picking them up, which takes time, or he's not using an automatic [or semiautomatic]. I don't think, in the dark, he's going to look down and try to find a shell casing that's 10 feet away from him ... "

However, if the gunman shot from an enclosed area, such as inside a vehicle, a shell casing might not be found.

Also, if a bolt-action or single-shot rifle was used, a shell would not be expelled, Abrams said. He also wondered why a sniper who has used a single shot to kill or wound his 11 victims would use a semiautomatic designed for fairly rapid firing.

Abrams said it would be possible for a knowledgeable witness to discern an "AK-style" weapon, short for "auto Kalashnikov." The features include a pistol grip, a magazine sticking out underneath and a relatively short length of about 3 1/2 feet.

But Abrams said, "There are more of this design of firearm in the long gun than any other in the world. They are basically as common as a Chevy sedan."

The AK-74 is one of 43 types of semiautomatic assault rifles banned in 1989 by President George Bush.

It is still possible to buy AK-74s that were in the country at the time, Abrams said, but buyers must pass state and federal background checks and wait eight days. Despite the import ban, he said, such guns are often smuggled into this country.

The difference between an AK-74 and an AK-47 is the cartridge it shoots, he said. Unlike the AK-47, the AK-74 can fire .223-caliber bullets - the type found at the scene of several shootings in the Washington area.