TACOMA, Wash., Oct. 23 -- The investigation into the sniperterrorizing the Washington area jumped across the country today as federal agents combed through a yard here, looking for shell casings and bullet fragments that may have been fired by a man police want to question in connection with the case, law enforcement sources said.

Agents armed with chain saws, metal detectors and heavy equipment removed a tree stump containing a bullet fragment and other evidence from the yard, officials said.

Startled neighbors said agents from the FBI and the federal Bureau of Alcohol, Tobacco and Firearms swarmed the home this morning.

FBI spokeswoman Melissa Mallon said the property owner consented to the search. She refused to say why agents were there.

A law enforcement source said the man police are looking for -- John Allen Muhammad, also known as John Allen Williams -- may have used the tree stump for target practice and investigators want to remove any bullets or bullet fragments to compare them with the .223 bullets used by the Washington sniper. Police said Muhammad may be traveling with a 17-year-old named Lee Malvo. A witness saw one of them firing an assault-type rifle at trees in the yard, according to a law enforcement source.

FBI agents also visited Bellingham High School, about 100 miles north of here, today seeking information on Malvo, who once attended the school, officials said. They also served search warrants in Alabama in connection with the same investigation, sources said.

Chris Waters, 23, a soldier at Fort Lewis, who lives across the street from the home, said today that in January he heard gunfire regularly at night, two or three shots at a time. "Every night, for about four weeks," he said.

Waters said he recognized them as high-velocity rounds. "This wasn't a handgun," he said.

About 15 agents worked throughout the day, at one point getting assistance from the Tacoma police department's bomb squad, according to Tacoma police.

"The focus of the investigation has been outside of the house," said James Mattheis, a police spokesman. "The focus has been on the yard."

A heavy array of equipment and vehicles, including tractors and U-Haul trailers, was at the scene in the 3300 block of South Proctor Street. Blue tarpaulin and rows of yellow tape, spaced at intervals of several feet, covered the yard. Neighbors saw investigators dig up a tree stump and throw debris that looked as if it was unearthed onto the tarpaulin.

By this evening -- about 7 p.m. Pacific time -- FBI agents were wrapping up the day-long operation and huddling outside the house. The stump was placed in the rear of a U-Haul truck and taken away. The yard seemed intact after the FBI left, with the area where the stump was removed, which is adjacent to a neighbor's garage, the only place that looked disturbed.

TV trucks, reporters and a few curious neighbors surrounded the one-story gray cement-block duplex.

The lawn outside is treeless and unkempt, and a burned two-door car sat tonight under a carport.

The blue-collar Oakland Madrona neighborhood in Tacoma is in the heart of the city, a transient area near major traffic arteries populated with residents of different races.

Houses in the neighborhood are small, mostly one-story and simple, with small yards. There are few trees, and many of the yards are bordered by metal fences.

Residents described it as a "so-so" place that sometimes has drug dealers, gunshots, pit-bull fights and flamed-out cars.

"We got good and we got bad," said resident Jana Watkins. "We've had our share of people down the street having dogfights. We've heard gunshots."

Fonofaavae Mulipola, whose aunt, Fonofaavae Tagoai, rents the house with the yard that was searched in the 3300 block of South Proctor Street, said about a dozen law enforcement officials flooded into the back yard about 9 a.m. They were still there when Mulipola returned home from work.

"It's kind of scary. We don't know what's going on in our own back yard," Mulipola said. "Friends and our family called us after seeing our house on the news asking us what's going on. But we can't even tell them."

Mulipola said her aunt and her two daughters have lived in the house for about 10 years. She said no one has ever done any shooting in her back yard, to her knowledge, and they have had no male visitors in the recent past, she said.

"This is a very nice, peaceful neighborhood," Mulipola said. "We've never had police come here, especially like this."

Special correspondent David Neiwert in Tacoma contributed to this report. Vogel reported from Washington, D.C.