The three recent high school graduates, in a Chrysler Sebring sedan, were coming home from a birthday party. The 55-year-old warehouse manager, driving a black BMW convertible, was returning from dinner and cards at a friend’s house.

Their vehicles collided head-on early Saturday in a fiery crash on a stretch of highway south of Crofton in Anne Arundel County, ending the lives of all four.

Maryland State Police said the car with the teens, with 19-year-old nursing student Brittany Ann Walker behind the wheel, was traveling the wrong way in the eastbound lanes of U.S. 50 when her vehicle slammed into the BMW driven by Terry Davis of Severna Park.

“It doesn’t make any sense,” Eduardo Lara, 54, Davis’s domestic partner of 31 years, said through tears. “How does this happen? I feel bad for their parents, but my God, what were these kids thinking?”

Investigators said Sunday that they had not yet determined why the car full of teens was on the wrong side of a divided highway that links Washington to Annapolis. Authorities said several motorists had dialed 911 in the minutes before the crash at 3:30 a.m., saying they saw a car speeding south in the northbound lanes of Interstate 97, and then in the eastbound lanes of U.S. 50 heading west.

State police said Sunday that the driver either crossed a median and turned around on the highway or took an exit ramp the wrong way.

A statement from police said they were not sure whether alcohol or high speed contributed to the crash. A duty sergeant at the Glen Burnie barracks said a small amount of marijuana was found in the Chrysler, but toxicology tests on the drivers and occupants were not completed Sunday.

The collision caused one car to burst into flames. All three teens died at the scene. Davis was pronounced dead at Anne Arundel Medical Center. Also killed in the Chrysler were Breanna Marie Franco and Zachary Tyler Rose, both 18.

In October, a state police officer pulled Walker over on Interstate 70 near Hagerstown, Md., after clocking her at 91 mph in a 65-mph zone. She pleaded guilty and paid a $290 fine, according to electronic court records.