A Philadelphia judge has ordered prosecutors to file charges against Brandon Bostian, the engineer who operated Amtrak 188 when the train derailed in May 2015, killing eight and injuring 200 others. 

Municipal Court Judge Marsha Neifield asked Thursday that authorities arrest Bostian and charge him with involuntary manslaughter and reckless endangerment after the family of one of the victims in the deadly wreck filed a private citizen complaint against Bostian.

The order reverses an announcement on Tuesday from the Philadelphia district attorney's office that it would not file charges against Bostian, citing insufficient evidence.

In particular, prosecutors said, there is not enough evidence to prove to a jury beyond a reasonable doubt that when Bostian sped into the Frankford Junction curve, he was consciously ignoring the risk of the action. That would be required under Pennsylvania law to convict him of criminal recklessness.

On Wednesday, the family of 39-year-old Rachel Jacobs, who was killed in the crash, filled out a private citizen criminal complaint, which the DA's office declined. The matter then moved to Neifield, who found there was probable cause to file charges against Bostian.

The decision came as a surprise to lawyer Tom Kline, who has represented the family of Jacobs and others in civil lawsuits stemming from the deadly crash.

"Most of the time, a judge will deny it," Kline said of private citizen complaints. "In this case, Judge Neifield didn't even hold a hearing. We presented our papers, and hours later, she ruled on our papers."

In a statement, Cameron Kline, a spokesman for the district attorney's office, said the matter has been referred to the Pennsylvania attorney general's office to "avoid the potential for any apparent conflict of interest."

State prosecutors can choose to pursue the case, or they can fight the judge's order by appealing to Superior Court.

Should the attorney general's office agree to charge Bostian, it would trigger a warrant for his arrest. Involuntary manslaughter carries a maximum possible punishment of five years in prison.

"Victims are wondering: How could it be that he not be held accountable? Not even a speeding ticket,” Mongeluzzi has said of Bostian. If someone was going 106 mph down Broad Street and killed eight and injured 230, they clearly would have been charged.”

Legal experts said a judge upholding a private citizen complaint after the district attorney's office declined to charge is unusual but not unheard of, although a more surprising outcome, they said, would be the attorney general's office deciding to prosecute Bostian.

"If the AG doesn't take the case, it's dead in the water," said longtime criminal defense attorney Perry de Marco Sr. "And the likelihood of the AG's office taking it is very slim."

Pennsylvania Attorney General Josh Shapiro confirmed that his office was examining the complaint against Bostian. 

De Marco added that appeals courts in Pennsylvania usually show deference to decisions made by prosecutors, so the liklihood of prevailing on appeal would be unlikely. 

The National Transportation Safety Board found that Bostian lost "situational awareness" on May 12, 2015, before he lost control of the train that flew off the tracks around a tight curve. Bostian was not under the influence of drugs at the time of the crash, nor was he distracted by his cellphone.

Investigators said he was likely preoccupied by a radio report that rocks were being hurled at another nearby train.

Since the derailment, Amtrak has taken responsibility and paid out $265 million in claims to victims. 

In additional, Amtrak has activated automatic-braking technology known as positive train control, which was not installed at the time of the incident.

Bostian has told investigators that he does not remember much about the moments before the wreck.

That, according to lawyer Robert Mongeluzzi who also represents victims, should not give him a pass.

"If we are to let operators off the hook with the mere claim of not having memory, then it invites every single one of them to do it," Mongeluzzi said at a Thursday press conference. "That's for a jury to decide in this case, as to whether or not Mr. Bostian is credible or incredible."