WASHINGTON -- At least a half-dozen top NFL health officials waged an improper, behind-the-scenes campaign last year to influence a major U.S. government research study on football and brain disease, congressional investigators have concluded in a new report.

The 91-page report describes how the NFL pressured the National Institutes of Health to strip the $16 million project from a prominent Boston University researcher and tried to redirect the money to members of the league's committee on brain injuries. The study was to have been funded out of a $30 million "unrestricted gift" the NFL gave the NIH in 2012.

After the NIH rebuffed the NFL's campaign to remove Robert Stern, an expert in neurodegenerative disease who has criticized the league, the NFL backed out of a signed agreement to pay for the study, the report shows. Taxpayers ended up bearing the cost instead.

The NFL's actions violated policies that prohibit private donors from interfering in the NIH peer-review process, the report concludes, and were part of a "long-standing pattern of attempts" by the league to shape concussion research for its own purposes.

"In this instance, our investigation has shown that while the NFL had been publicly proclaiming its role as funder and accelerator of important research, it was privately attempting to influence that research," the report states.

Democratic members of the House Committee on Energy and Commerce launched the investigation in December after Outside the Lines reported that the NFL backed out of the seven-year study, which aims to find methods for detecting -- in living patients -- chronic traumatic encephalopathy, or CTE, a disease found in dozens of deceased NFL players.

The report, first obtained by Outside the Lines, also shows:

• The co-chairman of the NFL's committee on brain injuries, Dr. Richard Ellenbogen, was one of the league's "primary advocates" opposing Stern, even though Ellenbogen had applied for the same grant and stood to benefit personally. Ellenbogen previously denied to Outside the Lines that he tried to influence the NIH, but the report sharply criticizes his actions.

• The NFL was warned that taxpayers would have to bear the cost of the $16 million study and that the NIH would be "unable to fund other meritorious research for several years" if the league backed out. The NFL offered a last-minute $2 million payment after an intermediary suggested a partial contribution would "help dampen criticism." The NIH turned down the offer.

• Even after an NIH review panel upheld the award to Stern, the NFL sought to funnel the $16 million to another project that would involve members of the league's brain injury committee. The plan would have allowed the NFL researchers to avoid the NIH's rigorous peer-review process. NIH Director Francis Collins rejected the idea.

U.S. Rep. Frank Pallone Jr., D-New Jersey, told Outside the Lines that the NFL's attempts to influence the NIH threatened to compromise the integrity of the research.

"Once you get anybody who's heavily involved with the NFL trying to influence what kind of research takes place, you break that chain that guarantees the integrity, and that's what I think is so crucial here," Pallone said. "Fortunately, the NIH didn't take the bait. It shouldn't be a rigged game. If it is, then people won't really know whether what we're finding through this research is accurate."

The NFL has repeatedly denied that it withheld funding because of objections to Stern, a professor of neurology and neurosurgery and the director of clinical research at Boston University's CTE Center. But in emails and phone calls documented by congressional investigators, league officials said they believed Stern was biased and his selection marred by a conflict of interest because a grant reviewer had previously appeared on a scientific paper with one of Stern's colleagues. The NIH ruled that the allegations were unfounded.

Jeff Miller, NFL executive vice president of health and safety, told investigators that the NFL voiced its concerns through appropriate channels and believed it had done nothing out of the ordinary.

NFL spokesman Brian McCarthy on Monday said: "The NFL rejects the allegations laid out ... There is no dispute that there were concerns raised about both the nature of the study in question and possible conflicts of interest. These concerns were raised for review and consideration through the appropriate channels. ... It is deeply disappointing the authors of the Staff Report would make allegations directed at doctors affiliated with the NFL Head, Neck and Spine Committee without ever speaking to them."

However, Dr. Walter Koroshetz, who directs the National Institute of Neurological Disorders and Stroke for the NIH, described the NFL's campaign as unprecedented, telling investigators he "was aware of no other instance" in which a private donor attempted to intervene in the NIH grant selection process.

NFL senior vice president of health and safety policy Jeff Miller was one of a half-dozen NFL staffers who tried improperly to influence a major U.S. government research study on football and brain disease, a Congressional report has found. AP Photo/David J. Phillip

"They wanted to look like the good guy, like they were giving money for this research," said Pallone, the ranking member on the Energy and Commerce Committee. "But as soon as they found out that it might be somebody who they don't like who's doing the research, they were reneging on their commitment, essentially."

According to a five-page research plan provided in the report, the NFL agreed to the objectives of the CTE study in July 2014 and committed $16,325,242 -- nearly the entire budget. The document was signed by NFL general counsel Jeff Pash, along with representatives of the NIH and the Foundation for the NIH (FNIH), a non-profit organization. In addition to raising money, the FNIH was created by Congress to help preserve the independence of the NIH, the nation's largest biomedical institution.

The report indicates the FNIH "failed" in that role, which resulted in the NFL "circumventing appropriate protocols of communication, attempting to influence NIH's selection of grant recipients and ultimately violating its obligation to provide funding for that grant." The FNIH had no immediate comment Monday.

The NFL first registered its concerns in spring 2015, after the NIH notified Stern that his group had been selected. As Outside the Lines has previously reported, a competing proposal for the grant was led by Kevin Guskiewicz, a prominent concussion researcher who chairs the NFL's Subcommittee on Safety Equipment and Playing Rules, and included three other NFL advisers, including Ellenbogen.

On June 17, Dr. Elliot Pellman, the NFL medical director who once ran the league's discredited concussion research program, emailed Dr. Maria Freire, FNIH executive director, to say the NFL had "significant concerns [regarding] BU and their ability to be unbiased and collaborative." He asked Freire to "slow down the process until we all have a chance to speak and figure this out."

Freire forwarded the email to Koroshetz.

"Yes, we knew this was coming," Koroshetz replied the next day, according to the report. "Lots of history here. But our process was not tainted and all above board. ... Trouble is of course that the [Stern] group is led by people who first broke the science open, and NFL owners and leadership think of them as the creators of the problem."

Less than a week later, the NFL's chief health and medical adviser, Dr. Betsy Nabel, emailed Koroshetz directly. She attached a 61-page affidavit that Stern had submitted in support of players who opposed the settlement of a class action lawsuit against the NFL in 2014.

"I hope this group is able to approach their research in an unbiased manner," Nabel wrote, according to the report.

On June 29, the FNIH arranged a conference call to discuss the NFL's objections. Along with Miller, the report states the NFL was represented by Ellenbogen and Dr. Hunt Batjer -- the co-chairmen of the Head, Neck and Spine Committee, which helps set league concussion policy -- and another committee member, Dr. Mitch Berger. (During Super Bowl week in February, Berger made headlines by saying he did not believe a link had been established between football and brain disease.)

On the conference call, the NFL raised concerns about Stern's alleged bias and the potential conflict of interest during the peer-review process.

The Congressional report is particularly critical of Dr. Richard Ellenbogen, who chairs the neurological surgery department at University of Washington, for intervening as both a grant applicant and a representative of the NFL. AP Photo/Doug Benc

Koroshetz told investigators that shortly thereafter, Ellenbogen called back to reiterate that "he could not recommend that the NFL fund the BU study, because he believed that Dr. Stern had a conflict of interest and that the grant application process had been tainted by bias."

Ellenbogen previously denied to Outside the Lines that he was part of any effort by the league to influence funding, saying that he doesn't know Stern "and therefore do not have an opinion of him."

The report is particularly critical of Ellenbogen, who chairs the neurological surgery department at University of Washington, for intervening as both a grant applicant and a representative of the NFL.

"Dr. Ellenbogen is a primary example of the conflicts of interest between his role as a researcher and his role as an NFL adviser," the report states. "He had been part of a group that applied for the $16 million grant. After his group was not selected, Dr. Ellenbogen became one of the NFL's primary advocates in expressing concerns surrounding the process with the BU grant selection. ... This series of events raises significant questions about Dr. Ellenbogen's own bias."

Through last fall, the NIH struggled to find out whether the NFL would honor its commitment to pay for the study.

"Clearly, it would be best if [the NIH] could count on the entire support from the NFL for the CTE project, as originally agreed," Freire wrote Miller on Oct. 19.

In a separate email, she noted, the NFL had put the NIH "in a difficult budgetary situation because this is a very large grant -- a cost that was not expected to be paid by taxpayers' dollars." Using public money would mean the NIH "will be unable to fund other meritorious research for several years."

Freire proposed that the NFL at least pay for the first year.

"Frankly, this would also be an important statement about NFL's commitment to research and will help dampen criticism," she wrote. "We understand that this is a very awkward situation all around, but some level of compromise would be the best possible solution."

Six weeks later, the NIH was still waiting on the league.

In December, days before the study was to be announced, the NFL offered to contribute $2 million, Miller told investigators.

At the same time, the NFL was continuing its efforts to redirect the $16 million to its own researchers, according to the report.

Another member of the Head, Neck and Spine Committee, Dr. Russell Lonser, a former NIH researcher, reached out to a senior NIH official to explore using the $16 million for a project that would involve the same NFL advisers. Under the plan, the researchers would not have been subjected to the NIH's peer-review process.

The report indicates Lonser's actions were "inappropriate" and "in direct contravention of NIH policy prohibiting donor involvement in the grant decision-making process."

The congressional investigators applaud the NIH leadership for maintaining "the integrity of the science and the grant-review process," but it adds that the NIH "may have gone too far in attempting to accommodate the NFL."

The report, which will be distributed to officials with the NFL, the NIH and the FNIH, recommends that the three groups amend their current agreement to ensure that "each party has a clear understanding of its role for the remainder of this partnership." The congressional committee will follow up with the NIH and the FNIH on its recommendations, which include establishing clearer guidelines for donors and communication with NIH officials.

The Stern study, which will include 50 researchers from 17 institutions and hundreds of former college and NFL players who will participate as subjects, officially launches next week in Boston.

On Tuesday, the NIH released a statement about the report: "This experience has reinforced the importance of clear lines of communication between NIH and FNIH. NIH has already taken a number of important steps to clarify its roles and responsibilities in agreements with FNIH and outside donors, in order to ensure that the science is free of even the perception of inappropriate outside influence."

Pallone told Outside the Lines the NFL's actions are particularly harmful to the league's players: "It says to them that they really can't trust the NFL to do the right thing."

NFLPA executive director DeMaurice Smith said on SportsCenter on Monday that the union decided, years ago, to split from the NFL on such matters because of the league's conflicted history around brain research. He said the league has no commitment to the health and safety of its players.

"It's one of the most troubling and disturbing reports I've seen," Smith said of the Outside the Lines story Monday, adding he wasn't surprised, however. "It reaffirms the fact that the league has its own view about how they care about players in the NFL."

Pallone said he hopes the report will push the league to make changes.

"The history with the league is, if you catch them, then they start to listen," Pallone said.