Fusion GPS co-founder Glenn Simpson struck a deal to appear before the House Intelligence Committee to participate in a voluntary, closed-door interview next week.

Committee members Reps. Mike Conaway (R-Texas) and Adam Schiff (D-Calif.) said during a joint statement that Simpson had been under subpoena by the committee as they seek more information about the “Steele dossier” on then-candidate Donald J. Trump, which Fusion GPS was involved in compiling and which is one of the controversial elements of the investigation into Russian interference in the 2016 election.

An attorney for Simpson announced that the executive will not assert his Fifth Amendment rights during the interview. Simpson and his lawyer, Joshua Levy, spent hours arranging the deal with the committee to allow Simpson to speak to members.

“He will be able to maintain Fusion GPS’s privileges and honor its legal obligations,” Levy told reporters. “That’s important to the company, which to this point has maintained its confidential relationships with its clients.”

Two other executives from the firm have already appeared before the committee, but both asserted their Fifth Amendment rights.

Levy says testifying voluntarily allows Simpson “the ability to appear with counsel, to assert privileges and to answer questions that he chooses to answer.”

According to The Hill, the Intelligence Committee is also seeking Fusion GPS bank records. A confidential deal was struck last week that will give them access to the records it seeks, according to the committee.

The Steele dossier was written by a former MI6 agent, Christopher Steele, and funded by twice-failed presidential candidate Hillary Clinton’s campaign and the Democratic National Committee.

Conservative website The Washington Free Beacon has also admitted that it hired Fusion GPS during the 2016 Republican presidential primary while conducting research on Trump, although their involvement ended before Steele became involved.

Republicans want to know who Steele’s sources were, who funded the document and how it has been used in the federal investigation, while Democrats say the real question is whether any of the claims made in the document are true.

According to The Washington Post: The  information included in the reports is mostly unverified “humint” — intelligence gathered by talking to people. As Wired noted shortly after the dossier was published, such intelligence will usually be flagged with indicators suggesting how credible the sources and claims should be considered. The dossier lacks that.

The Post concludes, after a lengthy evaluation, that much of the report’s claims are “rumors that couldn’t be independently verified.” Meanwhile, “many other claims” revolve around things that would have been publicly known or were “accurate predictions.”