An off-duty D.C. police detective was killed yesterday morning when another driver smashed into his Nissan at a red light on the Suitland Parkway, throwing the car into oncoming traffic and causing it to catch fire.

Eugene N. Lonon, 34, of Upper Marlboro was pronounced dead at the scene, near the parkway's intersection with Naylor Road SE, about 5:40 a.m. The driver who allegedly struck Lonon was charged with involuntary manslaughter.

Lonon was a 12-year veteran assigned to solve assaults, burglaries and other crimes in Southeast Washington's 7th Police District. A former homicide detective, he was remembered by colleagues yesterday as a quiet, dedicated investigator who, among other cases, helped solve the June 2000 killing of Grace Edwards, 76, who was shot in Southeast Washington as she took her morning walk.

"He was not a big talker, but he was methodical," said Cmdr. Winston Robinson, who oversees the 7th District. "When he completed the case, it was a very good case."

Daniel Friedman, a supervisor in the U.S. attorney's office, said Lonon "was a skilled interrogator, [and] he was dedicated to the case. His heart was totally in it."

Police said that Lonon had worked the midnight shift and had planned to run errands yesterday morning before appearing in court.

U.S. Park Police, who patrol the parkway, said Lonon was stopped in the eastbound lanes when a 1995 Mercedes-Benz driven by Michael Smalls, 40, of District Heights crashed into the back of his car. The impact caused Lonon's vehicle to catch fire and pushed it into the path of a westbound GMC Yukon. The Yukon struck Lonon's car and eventually caught fire, too.

Smalls was flown to Washington Hospital Center with minor injuries. The driver of the Yukon was taken to Prince George's Hospital Center in stable condition.

D.C. Police Chief Charles H. Ramsey said Lonon's brother Joe is a detective assigned to the 4th District in Northwest Washington. Ramsey said Eugene Lonon had two children, a daughter and an infant son.

The son is named Brian, Ramsey said, to honor Lonon's best friend, Brian T. Gibson, a District police officer who was shot to death at a Northwest Washington intersection in 1997.

"Now he's gone, too," Ramsey said. "And it's absolutely tragic."