Birgitta Jónsdóttir, the Icelandic MP and member of the WikiLeaks team that released secret footage of a US Apache helicopter attack on civilians in Iraq, is planning to visit America for the first time since the 'Collateral Murder' video was made public to express her support for Bradley Manning, the video's alleged source.

Jónsdóttir plans to travel to New York on 5 April to mark the third anniversary of the posting of the footage, one of the most dramatic WikiLeaks releases and one that helped put the website and its founder Julian Assange on the global map. She is making the journey even though she has been advised by the Icelandic government not to do so for fear of legal retribution from US authorities.

She told the Guardian that she had held back from visiting the US long enough. "I refuse to live in fear, and I don't want to live in the shadows. I don't think I've done anything illegal or that I'm an enemy of the US state, but if they think I've committed a crime, I want to know," she said.

Jónsdóttir plans to bring with her an exhibition of still photographs drawn from the Collateral Murder video that she will show in New York on the anniversary and Los Angeles on 6 April. Later, she hopes to take the exhibition on a road tour across the US on the eve of Manning's trial that is currently scheduled to begin in June.

The MP was part of a group of WikiLeaks volunteers who gathered in Iceland in early 2010 to help Assange prepare the footage of the Apache attack. Jónsdóttir organized the volunteers, researched details of the footage so that it could be annotated and selected stills for distribution to the media.

The footage, allegedly leaked by Manning while he was working as an intelligence analyst in a US base outside Baghdad, related to a US airstrike in Baghdad on 12 July 2007. Eight men were killed in the attack, including two Reuters correspondents whose cameras were mistaken for weapons.

The posting of the video had immediate and immense impact, prompting debate on the cost in civilian deaths of the Iraq war. A month later, Manning was arrested as the suspected source of the video along with hundreds of thousands of leaked confidential diplomatic cables.

The Iraq video has been cited in four of the 22 counts that Manning is facing, for which he faces up to life in military custody with no chance of parole.

Jónsdóttir said that she wanted to visit the US so that she could speak out about the importance of Collateral Murder in a way that Manning himself could not. "I feel connected to Bradley Manning's fate through that video," she said.

"It's deeply troubling to me that he is the only one suffering the consequences – none of the people responsible for the war crimes in the video have been held accountable."

For the past two years Jónsdóttir has been locked in legal dispute with the US Justice Department over its attempts to obtain her private information. It was revealed in 2011 that the US government had served a subpoena on Twitter demanding personal data from her Twitter feed dating back to November 2009.

Jónsdóttir riposted by petitioning a federal appeals court in Virginia, calling on the courts to force the DoJ to open its files on her to disclose the other internet providers that had also been ordered to submit her private data. Last month the appeal court ruled against her and her two co-defendants, allowing the US government to keep secret its attempts to force internet providers to hand over private information without a warrant.

In 2011 the US ambassador to Iceland gave verbal assurances that Jónsdóttir could travel freely to the US without fear of arrest or prosecution. But she has been advised by senior Icelandic government officials not to do so on the grounds that a verbal assurance is not binding and could be overruled by the US at any time.