Pants Left Behind Yielded Pivotal Link

No one put much stock in the initial discovery: a Marine dress cap and a pair of Marine dress trousers, found near the scene of a house fire in December in Arlington.

Never had the serial arsonist left behind anything more than the faintest forensic clue as to his identity. Why, after nearly two years of eluding investigators and frightening neighborhoods, would he give his trackers such a tantalizing, telling clue?

So far, no one is saying. But the items found near a white picket fence on North Bryan Street emerged yesterday as the crucial link. DNA found on the pants matched evidence obtained at several other arson scenes, all leading to Thomas A. Sweatt, 50, investigators said in announcing the arrest yesterday.

Before the string of arsons began, the Navy was looking into a series of suspicious fires near the Marine Barracks at Eighth and I streets SE. Navy investigators came to suspect Sweatt, who was acquainted with a Marine, but the fires around the barracks soon stopped and so did the investigation, authorities said.

The 46 fires that investigators suspect are the work of the serial arsonist, however, began several months later, in March 2003. An elderly woman died, other people were injured and communities were left on edge.

The search for the suspect included a reward, composite sketches, pleas to the public, a psychological profile. And at each crime scene, investigators combed for clues, hoping for the one that would be the key to the case.

In crimes as baffling and as long-running as this one, investigators seldom know what will turn out to be important and what will be inconsequential. Over time, several critical pieces of evidence were found, often connected to items of clothing, according to authorities.

"Nothing was overlooked at the scenes, ever," said Special Agent Theresa Stoop, the head of the Baltimore office of the Bureau of Alcohol, Tobacco, Firearms and Explosives, which was part of the regional task force assembled to track down the arsonist.

Not even when it seemed like a long shot, which is why fire investigators in Arlington listened to Alan J. Chaset.

Chaset lives across the street from the scene of the December fire and was out early that morning as investigators scoured the area for evidence.

"I walked over to one of the gentlemen and said, 'You might want to look at these pants because they weren't there last night when I walked my dog,' " said Chaset, 50, a criminal defense lawyer.

The case authorities have built against Sweatt relies on more than the distinctive red-striped trousers found by Chaset. The evidence outlined in an affidavit released yesterday begins Sept. 14, 2003, months after the serial arsons began, at a home on Anacostia Avenue NE.

The occupants returned from work early that morning and found an unfamiliar man sitting on their front steps. Though there had been no fire, the residents discovered a juice jug nearby containing what turned out to be gasoline, similar to the crude incendiary device the arsonist employed earlier. On the jug, investigators found a strand of human hair. A laboratory obtained a DNA profile from the hair sample.

It was the first of several DNA samples obtained by investigators, the building blocks of an investigation that at the time hardly seemed to be taking any shape.

The next would come on Feb. 14, 2004, in Silver Spring and also would involve a pair of pants. A fire had been set in the stairwell of a garden-style apartment building in the 7700 block of Blair Road. Along with a plastic jug, investigators recovered a piece of fabric from a pant leg. The fabric yielded DNA.

Then, on Sept. 20, another fire, this one in the District on 30th Street NE, yielded another clue. Along with the telltale plastic jug, investigators found the charred remains of a sock and were able to isolate DNA and obtain a profile.

And on Dec. 5 came the breakthrough where the fewest fires occurred. Only five of the arsons were in Virginia, compared with 21 in the District and 20 in Maryland.

After determining that the blaze was arson, Virginia investigators contacted the arson task force and eventually handed over the most curious pieces of evidence: the Marine pants and cap.

Sent to the ATF's laboratory and the Montgomery County police crime lab, the hat and pants were examined with no obvious urgency, two items in a long list of potential evidence.

In the meantime, the arsonist struck again Dec. 7, and once again, he left a crucial piece of evidence. After the fire, on 53rd Avenue in Bladensburg, investigators found a black plastic bag. Using some of the lettering on the bag, they were able to locate the bag's manufacturer, and learned that only two stores in the Washington area were supplied with the bags.

And then the DNA came back on the Marine trousers, matching the other three DNA samples. Sensing a bona fide break might be in reach, investigators contacted the Naval Criminal Investigative Service, which offered information about its earlier arson investigation at the Marine Barracks.

The man they had been looking at: Thomas Sweatt.

"We just got a lucky break," D.C. Police Chief Charles H. Ramsey said. "If it hadn't been for the Virginia fire and the Marine pants, and if the NCIS hadn't had the presence of mind to put that together even though it was a case that was 30 months old," there might not have been an arrest.

"If they hadn't taken the time to write all that down and who they stopped," Ramsey said, "we never would have known."