Investigators of Tuesday's deadly Amtrak derailment in Philadelphia reportedly have obtained a search warrant for the cell phone records of the train engineer in an effort to determine if he was distracted in the moments leading up to the fatal crash. 

The Philadelphia Inquirer reported late Thursday that city police had obtained the warrant for 32-year-old Brandon Bostian's phone records earlier in the day. 

Investigators also took issue with the characterization of Bostian's initial interview with investigators by the engineer's attorney. Robert Goggin told ABC News that Bostian had spoken with police for five hours before the attorney arrived to represent him Wednesday. However, the investigators told the Inquirer that Bostian had barely spoken with police before Goggin arrived and was only questioned by detectives briefly at a local hospital shortly after the crash.

Philadelphia Mayor Michael Nutter told reporters that Bostian had told detectives he did not want to be formally interviewed. "And he doesn't have to be interviewed if he doesn't want to be at this particular stage," Nutter said.

The Inquirer also reported that police officials had discussed the possibility of pressing charges against Bostian as early in the investigation as Wednesday morning. However, the Philadelphia District Attorney's office decided there had not been enough evidence collected to do so. 

More On This...

Eight people were killed and over 200 were injured when Northeast Regional 188 derailed shortly after leaving Philadelphia's 30th Street Station bound for New York. The National Transportation Safety Board revealed Thursday that the train had sped up from 70 mph until it reached more than 100 mph at a sharp bend where the maximum speed is supposed to be 50 mph.

NTSB member Robert Sumwalt said it was not immediately clear whether the train's speed had been increased manually by Bostian. He added that investigators have found no problems with the track, the signals or the locomotive, and the train was running on time.

Sumwalt also said that Bostian had agreed to be interviewed by the NTSB and that the meeting would take place in the next few days.

Officials believe they have now accounted for all 243 passengers and crew members who were thought to have been aboard, Nutter said. Forty-three remained hospitalized Thursday, according to the mayor. Temple University Hospital said it had six patients in critical condition, all of whom were expected to pull through.

Amtrak President and CEO Joseph Boardman said in a letter on Amtrak's official blog Thursday that it is cooperating fully with the investigation.

"With truly heavy hearts, we mourn those who died. Their loss leaves holes in the lives of their families and communities," Boardman wrote. "Amtrak takes full responsibility and deeply apologizes for our role in this tragic event."

He said the railroad's goal is "to fully understand what happened and how we can prevent a similar tragedy from occurring in the future."

Amtrak has said limited train service between Philadelphia and New York should resume on Monday, with full service by Tuesday.

The Associated Press contributed to this report. 

Click for more from Philly.com.