MINNEAPOLIS -- The two protesters who dangled from the rafters of U.S. Bank Stadium in protest on Sunday entered the stadium as ticketed guests and hid their climbing equipment under winter clothing, an investigation into the incident found.

SMG, which manages the stadium, said in a statement that the protesters brought nylon rope, carabiners and a banner through the gates at Sunday's Minnesota Vikings home game, getting through stadium security because they had "nothing visible in their possession that violated U.S. Bank Stadium policies and had nothing that prevented them from clearing the security screening upon entry."

Two protesters, Karl Zimmermann and Sen Holiday, climbed a ridge truss on the stadium's east side and swung from the rafters next to a banner that urged U.S. Bank Stadium to withdraw a credit line from Energy Transfer Partners, the company that is responsible for the Dakota Access Pipeline. The project is an underground pipeline for oil that crosses through four states, but protesters argue that it could damage the environment and poison the water in neighboring areas.

"The intruders gained unauthorized access to the ridge truss by scaling regulation standard physical barriers designed to prevent entry," SMG said in its statement. "We have taken immediate steps to implement design changes to prevent any future unauthorized access."

The protest, which occurred during the Vikings' 38-10 win over the Chicago Bears on Sunday, resulted in 185 fans being displaced from seats located directly beneath Zimmermann and Holiday. Vikings communications director Jeff Anderson said on Tuesday the team is contacting fans who were affected by the protest, offering a refund to the 71 season-ticket accounts that correspond to those seats, as well as affected fans who purchased seats through NFL Ticket Exchange.

"We are deeply concerned about Sunday's incident," the Vikings said in a statement. "The safety of our fans, players, coaches and game day staff is of the utmost importance. MSFA, SMG and Monterrey Security officials are currently leading the investigation to understand how this occurred."

Zimmermann, 32, and Holiday, 26, were booked into the Hennepin County jail on suspicion of gross misdemeanor burglary and trespassing, and were released on Monday afternoon. A third person, 27-year-old Carolyn Feldman, was issued a trespassing notice and released.

In a news conference on Tuesday, Zimmermann said the protesters had not been formally charged, but added he expected charges to be filed in the future. He repeatedly refused to answer questions about how the protesters got their equipment through security, saying he had been advised by his attorney -- whom he could not name -- not to discuss his actions.

Zimmermann would only discuss his opposition to U.S. Bank's involvement in the Dakota Access Pipeline, and said he was willing to go to jail in support of the cause.

Surveillance photos released by SMG showed Zimmermann and Holiday entering the stadium through the 95-foot-high glass doors on the stadium's west side. SMG said it expects to make additional security changes, and will continue to work with Minneapolis police to investigate the situation.

"It remains our intent to prosecute these individuals to the fullest extent of the law," the company said in its statement.

U.S. Bank Stadium will play host to Super Bowl LII in February 2018. NFL spokesman Brian McCarthy said the league "will review all aspects of the incident to understand how it occurred."