The crash killed McElroy as well as all three of his Coatesville High School classmates: Kyle P. Marsh, 17, and Evan S. Pringle, 15, both of Coatesville, and Jerry A. Warfel, 14, of Honey Brook.
Werner said McElroy was definitely speeding before he lost control of the vehicle. In fact, the 16-year-old had blown past an officer on routine speed-enforcement control on Route 82 without even realizing it, the chief said.
"He didn't even see him [the officer]," Werner said, adding that the officer clocked McElroy at 70 miles per hour in a 35 mph zone.
Seven-tenths of a mile and 41 seconds later, another motorist saw sparks coming from the underside of the teen's vehicle. Werner said the car likely "bottomed out" before running up an embankment, sliding sideways and hitting a tree.
"The roof was sheared off from the engine to the trunk," the chief said, adding none of the occupants were wearing seat belts.
Werner said the teens were coming from the Happy Days diner in Thorndale and were likely headed to one of the boys' homes.
Contact staff writer Kathleen Brady Shea at 610-696-3815, firstname.lastname@example.org, or @brandywinebits on Twitter. Read her blog, Chester County Inbox, at www.philly.com/chescoinbox.