The investigation, carried out by two Minneapolis attorneys, followed allegations made by former Vikings punter Chris Kluwe.
In a January essay for Deadspin, Kluwe contended that his 2013 release from the team was the result of his outspoken support for same-sex marriage.
He also said that former head coach Leslie Frazier pressured him to stop his public activism and that Priefer engaged in anti-gay taunts. Priefer repeatedly and vehemently denied the allegations, but the team's investigation concluded that the coach made a "single homophobic statement to Kluwe."
Vikings long snapper Cullen Loeffler confirmed Kluwe's account that Priefer once said, "We should round up all the gays, send them to an island, and then nuke it until it glows." Priefer owned up to the remark after Loeffler's confirmation, according to a summary of the report that was released by the team.
However, the investigators concluded that Kluwe was not released due to his activism, citing testimonials from other NFL talent-evaluators who agreed that the veteran punter's form had declined in his final season with the Vikings.
"There is consistent and weighty evidence from the record, mostly from Kluwe himself, that he viewed his performance as a member of the Vikings in an inflated manner," the report said.
It continued, "No interviewed witness agreed that Kluwe had a good year in 2012."
Along with the 29-page summary of the report, the team issued statements from Priefer and Vikings owner Zygi Wilf.
Priefer apologized to "the Wilf family, the Minnesota Vikings organization and fans, my family, the LGBT community, Chris Kluwe and anyone else that I offended with my insensitive remark."
Wilf said that Priefer will be suspended without pay for the first three games, though the suspension could be reduced by one game if the coach "satisfactorily" completes "specialized workplace training that will include an emphasis on the managing of diversity and sexual orientation."
The summary of the report also painted Kluwe in an unfavorable light, citing one example of a joke he made about disgraced former Penn State football coach Jerry Sandusky. The inclusion of those unflattering details prompted a defiant response from Kluwe on Twitter.
And yeah, if the Vikings want to play dirty, we can talk about ALL sorts of stuff.
— Chris Kluwe (@ChrisWarcraft) July 19, 2014
Kluwe's lawyer protested the findings, telling USA Today that he and his client requested a four game suspension for Priefer and a $1 million donation from the team to an LGBT rights charity. The team said it will make a $100,000 donation.
Kluwe and his lawyer plan to file a lawsuit against the Vikings next week, seeking $10 million in damages. The player said he will donate all of that money to charity.