An Oscar Award-winning filmmaker has finally learned why she was stopped whenever she returned to the US for more than 10 years.

Laura Poitras' travel nightmare began more than a decade ago when she first getting detained at airports every time she tried to set foot back in the country.

The 53-year-old was delayed without explanation more than 50 times on foreign travel, and dozens more times on domestic trips, before the extra searches suddenly ceased in 2012.

Only now, five years after the last stop, is Poitras beginning to unravel the mystery, which she has traced back to a bloody Baghdad day in 2004.

Filmmaker Laura Poitras (pictured in 2014) has learned she was delayed more than 50 times at US airports because of allegations she was involved in the ambush of a soldier in Iraq in 2004

Time after time, airport authorities searched her baggage, rummaged through her electronics and quizzed her for hours about her trips.

In Germany, she was told her name lights up 'like a Christmas tree' when security officials scan flight rosters.

In Austria, she was told her threat score was '400 out of 400.'

At John F. Kennedy International Airport in New York, her laptop, video camera, footage and cell phone were taken and held for 41 days.

In Newark, New Jersey, a security officer threatened to handcuff her for taking notes with a ballpoint pen that he said could be used as a weapon.

'I asked for crayons because I thought that would be less threatening to him as a weapon,' recounted Poitras, whose 2014 documentary film, Citizenfour, about the National Security Agency leaker Edward Snowden, won an Academy Award.

Poitras' travel nightmare began more than a decade ago when she first getting detained at airports every time she tried to set foot back in the country. She is pictured at the 2015 Academy Awards with (L-R) Dirk Wilutzky, Glenn Greenwald, Lindsay Mills, and filmmaker Mathilde Bonnefoy accepting the award for Best Documentary Feature

'He denied me any kind of writing device.'

Poitras, 53, knows US government officials are not exactly fans of her politically sensitive work.

Citizenfour depicted Poitras and journalist Glenn Greenwald's rendezvous with Snowden in a Hong Kong hotel where he handed over classified material documenting NSA's widespread surveillance program.

Her new film, 'Risk,' is about WikiLeaks founder Julian Assange.

Still, she never knew why the security delays started in 2006.

She unsuccessfully sought answers from the Homeland Security Department, before finally decided to take the government to court.

In 2015, she filed a Freedom of Information Act lawsuit in 2015 with help from the Electronic Frontier Foundation, a civil liberties advocacy organization.

Late last year, as a result of the suit, the government released more than 1,000 pages of documents to Poitras.

Poitras (pictured in 2015) was stopped without explanation more than 50 times on foreign travel, and dozens more times on domestic trips, before the extra searches stopped in 2012

The filmmaker, who won an Oscar for her movie, Citizenfour (left), has since learned she was the subject of extra security because of an allegation stemming from her 2004 project, My County My County (right)

The documents show for the first time the US government investigated Poitras on suspicion she might have been involved in an ambush that led to an American soldier's death in Iraq in 2004.

On November 20, 2004, Poitras was in Baghdad filming 'My Country, My Country.'

The film depicts Iraqi elections from the perspective of an Iraqi doctor, who criticized the American occupation yet hoped democracy would take root in his homeland.

Members of a US Army National Guard unit from Oregon reported seeing a 'white female' holding a camera on a rooftop just before they were attacked.

David Roustum, 22, an Army National Guardsman from West Seneca, New York, was killed. Several troops were wounded.

Some guardsmen who saw Poitras suspected she had a heads-up about the attack and didn't share that information with American forces because she wanted to film it.

If true, Poitras would have broken American criminal law.

The Academy Award winner called the allegation false and said she did not film the attack.

Documents show the US government investigated Poitras on suspicion she might have been involved in an ambush that led to an American soldier's death in Iraq in 2004. Pictured are soldiers after an attack in Fallujah in March 2004, where one US Marine was killed

Some guardsmen who saw Poitras with her camera suspected she had a heads-up about the attack and didn't share that information with American forces because she wanted to film it. Pictured are US troops after a Humvee was attacked in a shootout in March 2004

'There is no ambush footage,' Poitras told the Associated Press.

'That's the narrative that they created, but it doesn't correspond with any facts.'

After the attack, a lieutenant colonel, whose name was redacted from documents, reported the woman with a camera to his superiors. No action was taken.

But after returning home, the lieutenant colonel was contacted by author John Bruning of Dallas, Oregon, who was interviewing guardsmen for a book about their experiences in Iraq.

According to the government's documents, the author learned about the woman filming on the rooftop before the ambush.

In an email exchange on January 15, 2006, Poitras confirmed to Bruning she was filming in the area the day of the attack, but did not think she could help the author with his research.

'I was staying in the house of an Iraqi family I was following so my record of the fighting is from the perspective of the family,' Poitras wrote to Bruning.

'I did not venture out onto the street that day - didn't seem like it would have been a good idea. So I really don't have a document of what took place on the streets.'

Poitras said during one incident at John F. Kennedy International Airport in New York, her laptop, video camera, footage and cell phone were taken and held for 41 days. Pictured is the TSA screening area at the airport

This image shows a man holding a rifle in Poitras' 2004 film, My County My Country. She believes her security hassles stemmed from the filming of this movie

Bruning told the lieutenant colonel Poitras was the woman on the rooftop. The lieutenant colonel then informed the US military that she could have been involved.

In February 2006, a military police agent from Fort Lewis, Washington, interviewed the lieutenant colonel and the author.

Bruning declined to speak to the AP about Poitras.

But in his sworn statement to military investigators, he said he believed Poitras had prior knowledge of the attack.

He said Poitras was staying in a pro-Saddam Hussein neighborhood 'and she was not in fear of her life or being kidnapped at a time when Western journalists were being abducted and executed.'

Nevertheless, the Army Criminal Investigation Command at Fort Belvoir, Virginia, wrote a two-page letter shortly after to the FBI, saying the Army lacked sufficient evidence to charge Poitras.

The letter read: 'A review by our legal staff of the information developed thus far revealed credible information does not presently exist to believe Ms. Poitras committed a criminal offense; however, this could quickly change if Ms. Poitras were to be interviewed and admitted she had knowledge of the ambush and refused to notify U.S. forces in order to further her documentary and media interest.'

Poitras said she was never interviewed.

In May 2006, Army officials sent a summary of their investigation of Poitras to FBI headquarters in Washington.

The airport detentions and delays began shortly thereafter.

Poitras' award-winning documentary, Citizenfour, looked into the case of Edward Snowden. The NSA whistleblower is pictured in a scene from the movie with journalist Glenn Greenwald

Edward Snowden, Glenn Greenwald, David Miranda and Laura Poitras pose for a photo in Hong Kong

David Lapan, a Homeland Security Department spokesman, said other agencies control who is flagged as a high-risk traveler.

When people are flagged, he said, authorities must 'put them through enhanced screening procedures.

This is the reason for Ms. Poitras' repeated referrals to secondary screening.' The FBI, which had investigated Poitras, declined to comment.

The detentions stopped abruptly six years later after a 2012 news article highlighted her travel problems.

Lapan said Poitras was deemed no longer of 'significant interest.' That allowed Customs in June 2012 to 'discontinue its enhanced screening procedures,' he said.

Poitras worries her ordeal will resume, and as a result of her fears, she is seeking more information from the government.

A federal judge in Washington ruled last month the FBI hadn't provided adequate justification for withholding some information.

'I don't know if the investigation is ongoing,' she said. 'I don't know if it was ended or why it was ended.'

Her new film, Risk, will premiere on Showtime over the summer. At one point during a trailer for the documentary, a man is heard allegedly during a leaked FBI conversation describing her as 'anti-US'.