The mysterious boy on the Smithsonian laboratory table had probably died of pneumonia about 1850 -- too sick to eat, and delirious from fever.

His body had been dressed in a pleated shirt, finely tailored waistcoat and white sateen trousers and buried in an elegant iron coffin along Columbia Road NW in the District.

His remains were amazingly well preserved: He was five feet tall, dark haired and looked about 13. Beyond that, almost nothing was known. Who was he? Where had he lived? Why was he buried near a college in what was then the farm country well outside town?

This month, a team of experts at the National Museum of Natural History peered into his coffin for the first time in 150 years to try to unravel his story, perhaps learn more about his death and maybe something of his life.

The mystery began April 1 when his coffin was discovered by construction workers digging beneath a gas line outside 1465 Columbia Rd. NW in the Columbia Heights neighborhood.

The workers, unsure what to do, locked the coffin in an empty building where, on April 4, vandals broke in and smashed the coffin's glass faceplate and metal cover.

It was subsequently turned over to the Museum of Natural History, where a team of forensic anthropologists, pathologists, historical archaeologists, clothing experts and researchers began its work.

The coffin, which had been stored in a cooler, was opened Aug. 3. The boy's clothes were removed. An autopsy on the body was performed, and samples from his organs and strands of his hair were taken for further analysis.

Experts marveled at the preservation. The body's darkened flesh was still supple, they said, and the facial features were mostly intact. The coffin appears to have been sealed until the vandalism, but it's not entirely clear how that might have protected the body.

"We're still working on the exact reason these remains are so well preserved," said Larry W. Cartmell, an Oklahoma pathologist and expert on ancient diseases who helped perform the autopsy. "I don't think we have that mystery solved yet."

Arthur C. Aufderheide, a clinical pathologist and mummy expert at the University of Minnesota who also helped with the autopsy, said the boy's right lung tissue bore a peculiar redness and firmness often seen in cases of lobar pneumonia.

With modern antibiotics, such pneumonia now is unusual, Aufderheide said Tuesday. But it was common in the 1800s and was lethal among the very young and very old. He said the illness usually kills in about a week, before the immune system can counterattack.

He said the boy's empty stomach indicated he probably had not eaten for 24 to 36 hours.

"He may have been simply too sick," Aufderheide said. "These people become profoundly ill with lobar pneumonia. The temperature rises progressively, frequently up to 105. . . . If you're that sick, you're not interested in eating; in fact, you're probably delirious part of the time."

Cartmell said that the boy also had a cyst and other damage on the lung. Such damage suggested the pneumonia might have stemmed from a chronic respiratory ailment, such as tuberculosis. "He's had more or less chronic lung problems," Cartmell said.

Museum curators, meanwhile, studied the coffin, whose lid was shaped like that of an Egyptian mummy, molded in the shape of a flowing gown and marked on a raised area at the feet with the imprint of a mysterious flower.

"Isn't it nice?" lead anthropologist Douglas Owsley said in showing it.

This brand of coffin, which was expensive and advanced for its time, was first manufactured in 1849, historical archaeologist Deb Hull-Walski said.

"Typical coffin around this time period, wooden coffin, might cost a dollar and a half," Owsley said. This one probably cost $45 to $55. "A lot of money in that time period," he said.

It was originally polished and sealed with lead, Owsley said. The viewing glass allowed loved ones to see the deceased without being exposed to contagion, he said. There was most likely a name plate, now gone, fastened on the lid between two decorative motifs that survive.

Experts seeking the boy's identity said he might have been associated with nearby Columbian College, the precursor to George Washington University. A school history says the college had a small cemetery near Columbia Road.

Researchers last week were poring through archives and planned to scan old newspapers in search of death notices. "We're getting there," Hull-Walski said Monday.

Owsley said the boy might have been buried in the cemetery and been left behind when the cemetery was relocated. "They were very good at moving headstones," he said of such relocations. "They weren't necessarily so good at moving the people underneath the headstones."

The boy's clothing also was well preserved. The clothes were almost certainly his, and probably his Sunday best, Owsley said. Knowledge of teenage boys' clothing from that era is limited.

The boy was dressed "right as he would have walked out on the street," Owsley said, "how everything was put together."

On Monday, curators spread the clothing on a big table in Owsley's laboratory to be photographed. The clothes looked like those of a young squire: a trim, nicely cut vest with front pockets and cloth-covered buttons; a long, pleated shirt with collar and cuffs; socks; ankle-length underdrawers; and trousers that flared slightly at the bottom.

All were cotton, and probably a creamy white, said Shelly Foote, a retired clothing expert with the Smithsonian's Museum of American History. She pointed out that the buttons along the 27-inch waistline of the trousers were used to anchor suspenders as well as the loops attached to the top of the underwear. Elastic in clothing came in later, she said.

The trouser fly was fastened with metal buttons, she said: The zipper is a 20th-century invention.

There was a flurry of excitement Tuesday when someone spotted the initials I-I-O on the socks. But under a microscope it was clear that they were a manufacturer's mark cross-stitched into the fabric, not the embroidered initials of the owner, Foote said.

"These are the kinds of garments that any young man of his age and, probably, status would have worn," Foote said.

She said the narrow cut of the clothes suggested the early 1850s and guessed that the wearer was of the middle class, or higher, because of the well-tailored vest and the finer-quality cloth on the shirt collar and cuffs.

"It's so rare to see burial clothing intact," said Beth Eubanks, a textile expert working on the case. "Especially if it's a young boy, because there's not a whole lot of research that's been done on boys' clothing.

"It's a window," she said, through which "you don't normally get to see."

Forensic anthropologists Douglas Owsley and Kari Bruwelheide and others on the Smithsonian team examine the remains in the newly opened coffin.Textile expert Beth Eubanks examines the boy's shirt under ultraviolet light. "It's so rare to see burial clothing intact," she said.