Freshfields is flying a team of top lawyers to Florida this week to demand a retrial for a British national who has been on death row for 10 years.
The head of the firm's EU law litigation unit Paul Lomas and firm manager Jill Marsh will lead a team of lawyers working on a pro bono basis. The case is expected to incur a bill running into six figures.
Krishna Maharaj was convicted of murdering a Jamaican father and son.
The team from Freshfields is flying to Florida's capital Tallahassee to produce new evidence in the hope the case will be re-heard.
They will be joined by top civil liberties silk Geoffrey Robertson QC, head of Doughty Street chambers, Julian Knowles from Three Raymond Buildings, and Philip Sapsford QC from the Bar Human Rights Committee.
They are working with US lawyer Clive Stafford-Smith. It is expected that the state will call for the reimposition of Maharaj's death sentence after it was commuted in 1997.
Lomas, whose team is financially backed by Ernst & Young, says: "This case is unusual because he is almost certainly innocent. Freshfields has a pro bono panel and is doing quite a lot of work with the Bar Council's programme. We are also on the death row panel."
Freshfields lawyers hope to highlight four key claims about the case - that Maharaj had no history of violence, the murder victims were involved in money laundering, the main prosecution witness failed a lie detector test and that eight alibi witnesses can say Maharaj was not at the scene of the crime.
Freshfields also says that the judge in the original trial was arrested half way through and subsequently disbarred, leaving a new judge to take over, who had missed days worth of evidence.
UK-based law firms do work on death row cases in Commonwealth countries through the Privy Council, but the Privy Council is not involved in this case.
Lord Goodhart QC, the vice-chairman of campaign group Justice, is leading nearly 300 British politicians and peers who are supporting the effort.