ROCKVILLE, Md. (AP) - For the first time since the Washington-area sniper slayings began, more than one witness saw a man fire and flee in a white van, but investigators said Wednesday that none of the witnesses got a good enough look to yield a sketch.

“There are a couple of people who believe they saw a man shoot, unfortunately distance and darkness and perhaps adrenaline have made them unable to give a clear composite that we can disseminate,” said Montgomery County Police Capt. Nancy Demme.

Demme said one witness told police the shooter used an AK-74 rifle to kill 47-year-old FBI analyst Linda Franklin on Monday night outside a Falls Church, Va., Home Depot store.

“The witness firmly believes this is the weapon,” Demme said. “But we have to keep in mind that weapons are interchangable, like vehicles.”

Investigators said the latest shooting has yielded the most detailed clues yet in the search for the killer, including license plate information and a description of a man seen leaving the scene in a white, Chevy Astro van with a burned-out or broken left tail light.

With police unable to release more specific information, Demme gave a “how-to” list of tips for potential witnesses in case the sniper strikes again. Among them: commit to memory what you see, carry around a pen to make notes and, if necessary, write down descriptions and details on your hand. She also warned witnesses not to “contaminate” their remembrances by talking to other people or reporters.

Robert Young, a Washington construction worker, was among witnesses to Monday night’s shooting who returned to the shopping center Tuesday to talk with police. He said he heard a muffled gunshot and saw a white van.