The Manhattan District Attorney's Office sparked outrage this week when it announced it wouldn't file criminal charges against a taxi driver in a crash that severed a British tourist's leg.

By way of background: Sian Green of Leicester, England was struck when a taxi jumped a curb at Rockefeller Center on Aug. 20. Driver Mohammed Himon said he lost control after a cyclist slammed into the hood of his cab. Green lost part of her leg, and the NYPD mounted an investigation into the crash.

Soon after, the New York Post quoted Himon as saying he sped up to avoid a cyclist ("He was in my way and I got upset"), whom he went on to blame for the crash. But in the eyes of the prosecutor, Himon's actions failed to rise to the level of criminal behavior.

No criminal charges?! Why not?

The statement from the D.A.'s office would seem to indicate either a lack of evidence or a lack of confidence that the evidence would persuade a jury. Joan Vollero, a spokeswoman for Manhattan District Attorney Cy Vance, said in an email:

"Following a thorough, two-month-long investigation by the District Attorney’s Office and the NYPD, we have concluded that criminal charges cannot be filed in this case. In making this determination, prosecutors who are specially trained in vehicular crimes reviewed all available evidence and took into consideration relevant sections of the State’s Vehicle and Traffic Laws. They conducted interviews with multiple eyewitnesses, the taxi driver, the bicyclist, and injured parties, reviewed all available video surveillance, listened to numerous 911 calls, and retrieved the taxi’s ‘black box’ data.”

The District Attorney's office wouldn't respond to direct questions about the investigation — Was Himon speeding? What did witnesses say? — but Daniel Marchese, Sian Green's attorney, said in a statement that "the Assistant District Attorney...indicated that failure to charge was due to lack of evidence regarding the taxi cab drivers intent during the investigation phase."

What does that mean?

Joseph McCormack, a prosecutor in the Bronx D.A.'s office who is in charge of vehicular crimes, is not involved with the Himon case. But he pointed out the standards for criminal negligence are high. "There may be something that we may suspect, think or guess at," he said, "but that’s not what you need in court. You need evidence in court."

Also worth noting: last year, the NYPD told TN's Alex Goldmark that motorists need to break two traffic laws to rise to the level of criminality.

But Himon had a spotty driving record!

Doesn't matter. As far as determining whether a crime occurred, investigators typically look at what happened that day. "The fact that a person drove quickly six months ago doesn't necessarily mean that he drove quickly that day," said McCormack. "You would still need evidence relating to what happened that day — and it has to be evidence you can use."

Wasn't he suspended for a pattern of moving violations, though?

He was — but it was unrelated to the crash. Himon's license was suspended for 30 days due to points for previous traffic violations — but not until after the crash. (Due to a software glitch, the TLC had failed to flag up to 4,500 drivers who should have faced penalties. The TLC has said that problem has been corrected.)

Explain it to me again: isn't it a crime to drive into someone?

If they acted with criminal negligence or recklessness, yes -- but proving that requires "a pretty high level of egregious conduct," said McCormack. "What we look at in the criminal arena is when the mistake is greater than ordinary negligence and rises to criminal negligence. And what a defendant can be charged with depends on case law."

And case law is a product of society. The idea that traffic crashes are accidents, as opposed to preventable incidents, has been a pervasive one. This year, though, NYPD Commissioner Ray Kelly said the department was changing the name of the unit that investigates traffic crashes. What was once known as the Accident Investigation Squad is now the Collision Investigation Squad, because, as Kelly said, "in the past the term 'accident' has given the inaccurate impression or connotation that there is no fault or liability."

An official with the Manhattan D.A. said the office is always looking for ways to encourage changes in the law to make it easier to prosecute vehicular crimes.

Will Himon face any consequences?

Not criminal ones. Himon wasn't arrested by the NYPD at the scene of the crime, and his (unrelated) suspension is over. However, Sian Green's attorney said she is pursuing a civil suit against Mr. Himon.

What's the difference?

The burden of proof is different, as is the punishment. In a criminal case, a prosecutor brings action against the defendant, and the penalty can involve prison. In a civil case, the wronged party brings the action, and the penalty is typically monetary. In very watered-down terms, a civil lawsuit involves ordinary negligence. In criminal cases, it's criminal negligence  -- which has a higher degree of carelessness and risk-producing behavior than the civil standard.

And that is deeply unsatisfying to some. "There are 58 people who lose a limb or suffer another life-altering injury in this city every week due to traffic crashes," says Juan Martinez, a staff attorney with Transportation Alternatives. "And it’s just baffling that drivers like Himon escape public consequences for their actions." He added that a civil lawsuit is "a terrible way to get justice — it’s expensive, it’s time consuming, and it’s not justice at the end of the day. It’s some form of justice, but it’s not what we as a society expect to happen when somebody’s been harmed so egregiously."

"We need prosecutors to bring tough cases to fix the case law," he said. "And we need legislators to change the law."

Is Himon still driving a taxi?

As of this writing, he's not — but he could. "If there were no charges brought, there’s nothing upon which to predicate any action," said Allan Fromberg, a spokesman for the New York City Taxi and Limousine Commission, who said that Himon hasn't driven a cab since Oct. 31. 

(Note: this story was updated 11/18/13)