"It looked to us that the sergeant was trying to get away from him, but he constantly came at the sergeant with this knife," said Lt. William Gordon, a detective with the Upper Darby police. "He kept coming at him."
Sewell, an officer with SEPTA since 1982, had been sent by a foreman on the night shift to investigate a trespasser in the SEPTA garage lot, where about 100 buses are left for repair and cleaning.
The SEPTA foreman also called the Upper Darby police, Gordon said. Sewell, who had come on duty at midnight, called for a backup officer on his radio.
"Apparently, it happened very, very, very fast," Gordon said. "It was all over by the time the backup officers got there."
The second SEPTA officer arrived at the lot within minutes and heard the shots, said Donna Alston, a SEPTA spokeswoman.
By that time, a SEPTA mechanic who had witnessed the struggle told police, Sewell had found the man in the parking lot and put him up against the patrol car to search for weapons. It was then that the man spun around and started slashing the officer with a kitchen knife with an eight-inch blade, police said.
Evidence at the scene led investigators to believe that the man continued to pursue Sewell after at least the first shot from the officer's .38-caliber revolver.
Sewell fired several more shots, apparently on the run over a 30-foot area, Gordon said. The man was hit four times, in the chest and left arm, according to the medical examiner's report.
Sewell is the first officer to be killed on duty since SEPTA formed its police unit eight years ago, Alston said. The officer was promoted to the rank of sergeant in August 1987, she said. The unit has 130 officers.
Sewell, the youngest of six children, graduated from Upper Darby High School in 1976 and worked as a car mechanic before attending the Philadelphia Police Academy, said brother-in-law William Sides, a lieutenant with the Upper Darby police.
Sides said that, for as long as he had known Sewell - since 1974, when Sewell started dating Sides' sister, Jeanne - Sewell had wanted to be a police officer. He had hoped to join the Upper Darby force, Sides said, and was fifth on a list of qualified officers waiting for an opening.
Thomas and Jeanne Sewell, who married in 1981, bought a modest house with green shutters and a trim yard in Upper Darby last year and spent much of their free time renovating their home.
Several of Sewell's fellow officers, wearing black ribbons or tape across their badges, stood yesterday outside the SEPTA's 69th Street Terminal, around the corner from where the killing took place. They described Sewell as a ''gentleman" who treated his co-workers and the public with unfailing civility.
"We're a small department, so we're all taking it personally," Steven Snyder said. "He was a really private person and didn't let people get real close. But I can tell you one thing, he was an ace of a guy."
Sewell had recently been assigned to "property patrol," his co-workers said, a new beat to prevent thefts of SEPTA buses.
In the last four months, two buses have been stolen from SEPTA lots, resulting in serious traffic accidents as the thieves tried to escape. One of the buses was taken in December from the Victory Avenue lot where Sewell was killed, Alston said.
The duty is considered by some SEPTA officers to be less hazardous than patrolling the subways.
"Last night was a real freak thing," Snyder said. "This is not a high- crime area." Nevertheless, the terminal is "the end of the line" from Philadelphia, Snyder said, and it has become popular among the homeless who have been nudged out of city subway concourses and terminals.
Police suspect that the man who killed Sewell was homeless and think that he might have lived in the Philadelphia area, but he carried no identification. The Medical Examiner's Office has issued a description of the man and is seeking information from anyone who may be able to identify him.
The man was black, 20 to 30 years old, stood 6-foot-6 and weighed 193 pounds, said Steven Longbottom, an investigator with the Medical Examiner's Office. He was wearing a broad leather weight-lifting belt, inscribed in black ink with the letters "NEHS," which investigators said might refer to Northeast High School.
The man wore a gold stud earring in his left ear and a wristwatch with a black band. He had scars above both knees and on the back of his right hand. His hair was very closely cropped, and he wore a black coat, a black leather cap and a brown V-neck pullover. Under the sweater he wore two shirts, a gray button-down with green, pink and white vertical stripes, and a white shirt with blue pinstripes. He wore brown corduroy pants, a green leather belt in addition to the weight-lifting belt, and brown leather shoes.
Police have asked anyone who might have seen the man to call 891-5953.
"He could have been a vagrant," Gordon said. "We have no idea. No one knows what he was doing. He could have been sleeping in one of the buses."
A high fence topped with ominous curls of razor wire surrounds the bus lot, between the Cobbs Creek golf course and the intense commercial area along West Chester Pike in Upper Darby.
The detectives' chalk marks on the ground yesterday morning left surrealistic shadows of the struggle that had taken place between the two men in the dark. The bodies were outlined nearly foot to foot in front of the bus. The weapons were traced within inches of one another, but Ed Patton, SEPTA assistant superintendent for suburban operations, said that the knife, in fact, had fallen farther away from the gun, but when a SEPTA mechanic came upon the scene, he kicked it away from the body, not knowing whether the man was still alive.
"Lives taken for nothing," Patton said, looking over the ground, where the blood had been washed away.
SEPTA officers normally patrol alone but are kept within close range of a fellow officer who can respond to a radio call within minutes, Alston said.
This arrangement does not protect officers adequately, said several SEPTA officers interviewed yesterday. They said they had long thought that the solo patrols were dangerous; it is one of the issues being negotiated with the transportation agency.
Sewell's death, said fellow officer Michael Knoll, "stresses that some of these homeless are severely mentally ill. All we can do is shift them out of here. Upper Darby doesn't want to deal with them. They're not Upper Darby residents. It's a SEPTA problem."