Nearly two weeks after a deadly Amtrak derailment in Philadelphia killed 8 people and injured more than 200 others, investigators are still trying to piece together what led the train to enter a sharp curve at more than double the 50 mph speed limit.
The National Transportation Safety Board has ruled out the locomotive being hit by a bullet and is now focused on whether the engineer was using his cellphone while operating it.
Funerals have been held. Lawsuits have been filed. And all but a few of the most seriously injured remain hospitalized. Here are a few key questions and what we know right now:
WAS THE ENGINEER USING HIS CELLPHONE AT THE CONTROLS?
That's what the NTSB is trying to find out.
The agency says investigators are comparing time stamps from engineer Brandon Bostian's phone records with locomotive data, radio transmissions and surveillance video to see whether the phone was used while the train was in motion.
Phone records show the phone was used to make calls, sent text messages and access data the day of the derailment, but it's unclear when. Bostian's lawyer says the phone was switched off and kept in a bag and he used it afterward only to dial 911.
Engineers aren't allowed to use phones while operating trains or preparing them for movement.
WHAT WAS THE ENGINEER'S DAY LIKE BEFORE THE CRASH?
The first leg of Bostian's shift on May 12 was particularly grueling, union officials say, with equipment-related delays on his train to Washington shortening his rest break.
A system displaying track signals on the dashboard failed, forcing Bostian to pay close attention while reducing speeds far below normal, according to Railroad Workers United.
The train reached Washington 26 minutes late, leaving Bostian about an hour to rest, eat and use the restroom before his trip back to New York on the train that eventually derailed.
Bostian told investigators he didn't feel fatigued or ill prior to the derailment, the NTSB says. His lawyer, Robert Goggin, says he had no health issues and wasn't taking any medication.
DID THE ENGINEER KNOW THE ROUTE?
Yes. Bostian was an engineer on the Northeast Corridor for about three years and was assigned to the Washington-to-New York route for several weeks before the derailment, the NTSB said.
He worked a five-day-a-week schedule, making a daily roundtrip from New York to Washington, and had a "very good working knowledge'' of the territory and various speed restrictions, NTSB board member Robert Sumwalt said.
As part of his training, experts say, he would have shadowed veteran engineers and been graded on his performance navigating curves and speed restrictions before being qualified to work the route alone.
WHY ALL THIS FOCUS ON THE ENGINEER?
Bostian was alone at the controls as the train rapidly increased speed heading into a sharp curve, so his actions and recollection of the moments leading to the derailment are critical.
There's no explanation for why the train went from 70 mph about a minute before the crash to 106 mph a few seconds before it left the tracks.
Investigators say preliminary inspections found no problems with the track, the signals or the locomotive.
They've also ruled out a bullet causing a grapefruit-size fracture on the locomotive's windshield and say they're uncertain whether anything struck the train.
It's unclear whether Bostian manually accelerated, Sumwalt said, though a data recorder shows that he did engage a braking system seconds before the derailment.
Bostian, who was injured, told investigators May 15 he didn't remember anything after ringing the train's bell while passing through a commuter rail station about 3 miles from the crash site, the agency said.
That's different from what his lawyer told ABC News the day after the crash. Goggin said Bostian recalled that the train was "pulling into speed-restricted track'' but did not remember activating the emergency brake, as depicted on video from inside the cab.
Goggin said his client voluntarily submitted to a blood test and wasn't under the influence of drugs or alcohol.
WHAT ABOUT THE VICTIMS?
Funerals have been held for several victims, including Naval Academy midshipman Justin Zemser and educational technology executive Rachel Jacobs. Others are being planned.
The family of Italian wine and olive oil broker Giuseppe Piras says it's having trouble returning his body to his homeland, in part because his body was moved to a New Jersey funeral home from Philadelphia without permission.
Several people injured in the derailment remained hospitalized as of Friday.
The conductor and nine passengers have sued Amtrak over the crash, and Sen. Bill Nelson, D-Florida, has introduced legislation that would increase the limit on damages Amtrak could be forced to pay from $200 million to $500 million.