IN ONE way it could seem like one of the more straightforward incidents police have to deal with.

Eleven men killed by a plane crashing into a road. Identity of lone pilot not in dispute. Tens of thousands of witnesses.

Yet rather than having to establish the usual facts of who and what, investigators are trying to find out why.

Was there something wrong with the plane? Did the pilot make a mistake? Could any part of what happened amount to a criminal offence?

Those much more difficult questions have so far taken Sussex Police across thousands of pieces of evidence and into the unchartered territory of aviation rules and procedure.

“It is very clear what happened in terms of the crash and the huge devastation it caused – everyone has seen that,”said Steve Whitton, the acting assistant chief constable for Sussex Police overseeing the Shoreham investigation.

“What is not clear is why it happened and how,” he added.

"Which is obviously the focus of our investigation."

"And it is really important we get that right, which is why it takes time. It has been a steep learning curve.”

Since the six-tonne Hawker Hunter flown by Andy Hill crashed into the A27 on Saturday, August 22 last year, police have taken statements from more than 350 witnesses, taken in 4,000 documents and pieces of evidence, and received video evidence from more than 200 people.

A team of six officers as well as lead detective Paul Rymarz and his deputy are now working on the investigation.

When they consider their work done, they will pass what they have learned to the coroner for the men’s inquests, but also potentially to the Crown Prosecution Service which will decide if any charges should be brought.

They told Mr Hill in December that he is being investigated for possible endangerment under Article 138 of the Air Navigation Order 2009, and also manslaughter by gross negligence.

Detectives have widened their investigation beyond the Hawker Hunter's doomed Shoreham flight to try and answer what went wrong.

One of Mr Hill’s previous air-show display is line of enquiry in their investigation: during the Southport Airshow in 2014, he was asked to stop his display after the flight director deemed he was flying too low and too close to the crowd.

Mr Whitton would not say whether detectives are looking at other airshows or individuals, only that the investigation is complex.

He said: “There are various aspects to the investigation and it’s not appropriate to talk about specific parts of that.

“We have been working extensively to gather all the information and evidence that we feel is appropriate for the investigation.

“This is a very wide-reaching investigation around the whole circumstances. Certainly we have not closed down any lines of enquiry.

“We keep an open mind and continue to make sure that we can do all we can to get the answers that we need and that are needed.”

Adding to that scope is the different aims of police and air accident investigators looking into the crash.

Police are looking to find out whether anyone committed an offence, while the Air Accidents Investigation Branch (AAIB) is trying to find lessons for air safety.

Evidence gathered by air accident investigators is legally protected by default – because they want to encourage people to come forward about crashes to them knowing information will not necessarily be passed to police.

Officers therefore have to go to the High Court for that evidence, and are currently awaiting the result of a hearing held on July 14.

They have applied for evidence around the Hawker Hunter's flight including cockpit recorders and footage, witness accounts, expert reports and documentation.

Lord Chief Justice Lord Thomas and Mr Justice Singh are deciding whether the benefits of disclosure outweigh any adverse domestic and international impact that such action may have on that or any future safety investigation.

There is no indication of when they might make their decision but lawyers for some of the families have said the process might delay the criminal investigation until Christmas.

Despite this delay the last 13 months have not been without information about what happened.

The wreckage of the 45-foot, four-foot tall Hawker Hunter, which has a 33-foot wingspan, was taken to Farnborough, Hampshire, for analysis.

In September the AAIB said "no abnormal indications" were identified from the plane, and that it appeared to be responding to the pilot’s "control inputs" throughout the flight.

The plane’s owners, Canfield Hunter Ltd, have settled two compensation claims so far, lawyers for the victims' families said yesterday (Friday).

Canfield Hunter said its admission of liability was a statutory requirement, and it was committed to helping those caught up in the tragedy.

The AAIB is due to release its full report later this year, and Mr Whitton said once the High Court decision is made, the end might be in sight for the police investigation.

“This is the proper judicial process because of the wider significance of obtaining protected material from an organisation such as the AAIB,” he said

“It is absolutely right this happens.

“Once a decision is made from the High Court. I will be at a better stage to actually start saying well we know how long it is going to take.

“Of course it is frustrating to everyone that we cannot complete this, particularly of course because at the heart of this is the families, and we want to be able to get the answers that the families need.

“But it is important that we get it right, and that we take the time that is needed to get it right.

“I think we are doing all we can to move this investigation forward and I am very confident in the senior investigating officer and the team.

“But I am very conscious of the fact the families have suffered a huge tragedy, a significant loss which is going to be affecting them every single day of the week.”