Federal investigators will focus on how much the electrified third rail compounded the damage in Tuesday's fatal Metro-North crash in Westchester County and whether the SUV driver stuck on the tracks was familiar with her vehicle.

National Transportation Safety Board member Robert Sumwalt said Thursday the construction of Metro-North Railroad's electrified third rail differs from other third rails. The electric element is sandwiched between a top shoe and a bottom shoe, and investigators want to look at whether this design contributed to the disintegration of the third rail, which then thrust through the SUV and train car. Five men in the train and the SUV driver were killed. At least 10 were injured, and of those five remain at Westchester Medical Center.

He also said the Mercedes-Benz SUV driver, Ellen Brody, 49, of Scarsdale, had not owned her car for long, and investigators want to look into how familiar she was with the operation of the vehicle.

"We have a mosaic and we're going to take different pieces of information, pull it together . . . and see what that picture looks like," Sumwalt said at a news conference.

Investigators wrapped up their first interview with the train engineer moments before Sumwalt spoke Thursday. He gave one important detail from the interview: "The engineer reported he saw the car go on the tracks."

Sumwalt said all equipment appeared to be working properly, from the brightness of the lights on the crossing gate in Valhalla to the series of horn blasts the engineer, traveling 58 mph in a 60 mph zone, sounded right before the crash.

When the engineer saw the SUV, he applied the emergency brakes, the investigator said. The train came to a stop almost 30 seconds and 950 feet later, he said.

Traffic crossing the rail line was jammed due to a nearby accident.

The motorist behind Brody said as he approached the crossing the traffic was "inching along."

Sumwalt said the man saw the crossing gate lower and hit the SUV. He told investigators she examined the damage, then went back into the SUV and "suddenly pulled forward" into the path of the train, Sumwalt said.

"We're combing carefully through ash, debris and pieces of third rail that have penetrated through the rail car. . . . We're looking for the crash worthiness of the car and we're looking for information to help with the fire science analysis of that car."

Sumwalt said investigators will come up with a timeline of what happened, including when the crossing gates came down.

Also Thursday, regular Harlem Line service resumed with the morning rush-hour, two days after six people died in the fiery crash.

Damage to the third rail ignited a "fierce fire," investigators said Wednesday.

About 400 feet of the third rail, coated with gasoline from the SUV, broke apart in about 80-foot sections that were "shoved into mostly the first rail car and at least one piece penetrated the second rail car," sparking the inferno, investigators have said.

"The entire interior of the first rail car was burned out," Sumwalt had said Wednesday. The charred remains of the train were moved to a storage yard for investigators.

Crews worked overnight Wednesday to remove the train cars involved in the accident and repair the broken third rail, according to Aaron Donovan, an MTA spokesman. The Harlem line reopened Thursday morning.

MTA spokesman Aaron Donovan on Thursday said the five men who died on the train are Robert Michael Dirks of Chappaqua, Walter Liedtke of Bedford Hills, Joseph Nadol of Ossining, Aditya Tomar of Danbury, Connecticut, and Eric Vandercar of Bedford Hills.

Train passenger Liedtke, 69, was a renowned curator at the Metropolitan Museum of Art with an expertise in Dutch and Flemish art, and passenger Vandercar, 53, was a financial manager at Mesirow Financial in Manhattan, family and friends said.

Two of the victims -- Nadol and Tomar -- worked for J.P. Morgan Chase & Co., the company confirmed Thursday.

"It is heartbreaking . . . that two J.P. Morgan employees were among the victims of this week's tragic Metro-North train accident," a spokeswoman said in a statement. "Our thoughts and prayers go out to their families, and to the many employees who worked with these colleagues and knew them well. It is a terrible tragedy and loss."

Employers and family members said that Dirks, 36, of Chappaqua, was a research scientist at D.E. Shaw Research in Manhattan.

Speaking to reporters after a presentation at Farmingdale State College on Thursday, Gov. Andrew M. Cuomo spoke about the "unbearable" grief the families of those killed must be going through, drawing parallels with the recent death of his father, former Gov. Mario Cuomo.

"From my point of view if there was any mistake or error on behalf of the MTA . . . we want to know about it," Cuomo said. "If there is something we can learn from here, we would want to know about it obviously."

On Wednesday investigators began poring over the burned-out train, which had held hundreds of people during the crash, and took away the SUV.

A county police helicopter used infrared thermal imaging to search the hills and the snow for possible victims who might have wandered into the nearby cemetery and collapsed from their injuries, but the aircraft found no one, Valhalla Fire Chief Roger King said.

Examining crash factors

Investigators are focusing on the potential for driver error, lighting at the crossing, the gate itself and the third rail, among other factors, Sens. Charles Schumer (D-N.Y.) and Richard Blumenthal (D-Conn.) said in a conference call.

Schumer said the MTA and the Federal Railroad Administration are also conducting their own probes. He said the fact there may have been traffic at the Westchester crossing at the time because cars were being diverted from another road also "may have had something to do with this."

According to Sumwalt and King, who had just responded to this accident, a head-on collision on the Taconic State Parkway and Lakeview Avenue earlier was causing congestion on Commerce Street around that time.

Sumwalt said the two major questions are what was the vehicle doing in the crossing and what effect, if any, did the traffic detour play in this crash.

The train was traveling about 58 mph, within the limits, when it "bulldozed the car for quite a distance," Schumer said.

Blumenthal, like Schumer, said he will push for fast answers from investigators.

"This kind of horrific, terrible crash was preventable -- that's the lesson here," Blumenthal said. "It was preventable with the right kind of equipment, functioning properly, and the right kind of behavior on the part of either the driver of the car, the driver of the train, and others involved."

He also said that "clearly, if a driver recklessly or needlessly crossed that guard at a time when it was indicating that there was a danger in doing so, we need to know about it, so others will be educated and made aware about those dangers."

Sumwalt said the NTSB would likely be at the scene for about a week, "collecting perishable evidence, evidence that can go away with the passage of time."

He said investigators hope to interview the train's operators within 24 to 48 hours, understanding that they've been through emotional and maybe physical trauma.

"We want to make sure they're in a position that they can comfortably speak to investigators -- but that's a high priority," he said.

Recorders should help

Recorders on the trains, signals and crossing gates should also help investigators determine what happened and whether there was a change in the train's speed, a whistle blown, and when the gates and signals were activated.

MTA chairman and chief executive Thomas Prendergast and Metro-North president Joseph Giulietti are working in collaboration with the NTSB on the probe, the MTA said in a statement.

"The entire MTA family's thoughts are with the relatives and loved ones of the victims of last night's tragedy," Prendergast said on Wednesday.

"We are tremendously saddened by this tragic accident, and our thoughts and prayers go out to all of them. We also thank the first responders who assisted with safely removing the passengers from the trains and transporting those who were injured to area hospitals."

The conductor and engineer were both injured, Donovan said, but he was unsure the extent of their injuries or whether they were hospitalized.

Westchester County Executive Rob Astorino said Wednesday that all except one of the people who died "were burned beyond recognition, so we're going to need dental records to try to identify the bodies."

Many of the victims were from Westchester, he said later Wednesday at the Westchester Medical Center campus.

"They have an idea of who all the victims are, but until they get a positive identification through the records," names will not be released, Astorino said.

Astorino said he met with the wife of a victim from the Town of New Castle. "She's in total shock," Astorino said. "She obviously saw what happened last night. She didn't get a call, her husband didn't return home. She then called the police and she was asked to bring the records in."

The NTSB is scheduled to host a news conference late Thursday afternoon in Tarrytown, said Weiss, spokesman for the agency.