William Key said he glanced up just seconds before the car crash unfolded in Oxon Hill on Friday night — a wreck so bad it would take the lives of two children and three adults and prompt one fire official to call it one of the worst he has seen in 40 years.

According to Key, a speeding Mercedes-Benz swerved around a westbound bus picking up passengers on Livingston Road around 9:40 p.m. and shot through a red light, narrowly missing a woman and child.

At the intersection of Livingston Terrace, the car plowed into the back of an Acura carrying five people. The Acura was making a right turn on red at the time.

“It was indescribable,” Key said of the impact’s deafening boom. “It was too hard. My wife heard it at home two blocks away.”

The aftermath would be even more horrific. Key said the Mercedes was sent spinning and then burst into flames. The driver of the Acura and a passenger, ejected from the car, lay writhing on the street.

A makeshift memorial is set up at the site of Friday night's fatal car crash in Oxon Hill. (Justin Jouvenal/The Washington Post)

Key said he watched as the driver of the Mercedes and a passenger scrambled out of their flaming vehicle. The driver crawled away from the scene on his elbows, Key said.

The wreck claimed the lives of everyone in the Acura except for the driver, who remained in guarded condition at a hospital. One female passenger was pronounced dead at the scene. A second woman and two children were rushed to a hospital, where they died of their injuries.

The driver of the Mercedes was taken to a hospital, where he remained in critical condition. A female passenger was pronounced dead at the scene, and a second passenger was being treated for injuries not believed to be life-threatening.

Police are withholding the names of the victims pending notification of next of kin. On Saturday evening, investigators were still looking into the crash’s cause but said speed and the weather may have been factors.

Authorities said it remained unclear why the Mercedes ran through the intersection, but Maria McKinney of Prince George’s County police said the vehicle was not being chased by police.

Key, of Oxon Hill, said he wanted to help the victims but that an unmarked police car arrived at the scene soon after the wreck and an officer told him to stay back. The Acura, its back end crushed, had come to rest on the grassy side of the road, next to a telephone pole it had apparently struck.

The Mercedes was about 100 feet down the road, with its front end smashed in.

“I’ve been in the county since the 1990s, and in terms of victims, it is one of the highest I’ve seen in a long while,” said Assistant Fire Chief Paul Gomez.

The fire department’s spokesman tweeted that it was one of the worst in four decades.

The force of the crash was still apparent Saturday morning. The telephone pole struck by the Acura was splintered and listing precariously, like a broken toothpick. Someone had propped a copy of “The Cat in the Hat” and a doll against the pole as a memorial.

Several residents of the area said that the bustling intersection where the crash occurred has been the scene of other wrecks and that they believe it is unsafe. One said he had been hit by a car there three years ago.

Livingston Road and Livingston Terrace form a T-intersection in the area, just a short distance from Indian Head Highway. On one side of Livingston Road, there is a large apartment complex; on the other is a busy strip mall. There are numerous pedestrians in the area, but the crosswalk has faded.

Key was so affected by the crash that he bought a bouquet of pink flowers and placed it at the base of the telephone pole with the book and doll. When Key was told by a reporter that five people had died in the crash, tears welled up in his eyes and he turned away.

When he regained his composure, he said simply: “This is a bad intersection.”