Federal investigators completed their on-scene work yesterday in the investigation of last week's tanker explosion on Interstate 95, returning to their offices with reams of evidence and witness statements but no clear explanation for the crash that took four lives.
Authorities have not publicly ruled out any potential cause - from driver error to mechanical failure - but officials familiar with the investigation said that medical emergency is emerging as a leading theory.
"Witness statements and erratic behavior would lead us to believe a natural event is what we want to strongly consider," said David Fowler, the state's chief medical examiner, who performed an autopsy on the tanker driver and other victims.
A witness reported seeing the tanker driver slumped over the steering wheel of his truck seconds before it left the road. National Transportation Safety Board investigators tested that account Saturday, shutting down a section of Interstate 895 to reconstruct the Jan. 13 crash.
The investigators pulled a four-door Pontiac up to the side of a replica tanker for a "sight distance" test to determine whether it was possible for a witness to see the tanker driver. Several investigators who took turns sitting in the driver's seat of the Pontiac declined to comment on the results of the test.
Authorities were awaiting yesterday the results of toxicology tests of a blood sample taken from the body of the tanker driver, Jackie M. Frost, 64, of Finksburg. Two witnesses told police they saw Frost's tanker moving erratically on I-895 before the crash.
Fowler said there is no definitive test to determine whether someone has suffered a heart attack. But certain conditions, such as a narrowing of the blood vessels, can suggest such a possibility.
Maryland Transportation Authority Police Chief Gary W. McLhinney said all reasonable theories are being considered. "The investigators are looking at everything," he said. "It might not be a single factor. It could be some kind of medical event combined with failure of the vehicle to perform properly."
One early theory of the crash was that shifting of fuel in the tanker caused it to go out of control and fall from I-895 south onto I-95 north in Elkridge. That theory fell out of favor when investigators learned that the tanker had been nearly full.
NTSB spokesman Ted Lopatkiewicz said investigators have spent this week taking further measurements from the highway and the remains of the tanker to get enough data to create a computer-animated reconstruction of the accident. He said the front and cab of the tanker are in better condition than the rear.
"There's no doubt that it makes it harder to do the job because of the severe fire damage," Lopatkiewicz said.
The others killed in the crash were tractor-trailer driver Rita Ann Gull, 42, of Lansing, Mich.; pickup truck driver Maurice Durschlag, 62, of Glen Burnie; and a taxi driver whose identity has not been confirmed. Friends of Red Ball cabdriver Marc Baladi, 63, have said they believe that he died in the crash.
Maryland Transportation Authority Police, who are leading the investigation, say they are awaiting DNA test results to confirm the identity of the taxi driver.