U.S. Park Police are trying to track down people who might have seen the driver killed in a crash Tuesday on the Baltimore Washington Parkway minutes before the crash happened.

In particular, police are trying to get in contact with a woman who called 911 shortly before the 6:20 p.m. crash to report she had seen a man on the side of the road apparently arguing with another person, said Sgt. David Schlosser, a U.S. Park Police spokesman.

The woman’s call to 911 was dropped before police could get her contact information, Schlosser said.

Police believe the man the caller saw might have been 34-year-old William K. Ward, of D.C., who was killed after his Kia Optima sped into another car headed north on the Baltimore Washington Parkway between Riverdale and Good Luck roads, then careened into a tree, Schlosser said. The man in the other car sustained only minor injuries, Schlosser said.

Speed was an obvious factor in causing the crash, Schlosser said. Investigators are still awaiting toxicology results to determine whether drugs or alcohol were also factors, he said.

Schlosser said that in addition to looking for the woman, police are also seeking witnesses who might have seen Ward’s car traveling slowly, then fast and recklessly, in the moments before the crash. He declined to say whether detectives had tracked down the other person the woman saw in the dispute.

Anyone with information is asked to called the U.S. Park Police’s Criminal Investigations Branch Tip Line at 202-610-8737.