A man who climbed under the roof of the Dortmund stadium during Germany's European Championship round of 16 match on Saturday was masked and carrying a large rucksack, according to video footage.
The video, published by the website of English newspaper the Daily Mail, shows the man being arrested by police at gunpoint after the match against Denmark.
Officers announced that the man was a 21-year-old from the German city of Osnabrück, around 120 kilometres north of Dortmund.
Police said there had been no danger to spectators but did not reveal how he entered the stadium, what was in the rucksack, why he was balancing on the beams holding up the roof and why he wore a mask.
A helicopter was used to illuminate the stadium roof as part of the bid to seize him once the majority of fans had left following Germany's 2-0 win.
He got under the roof during the game and both sets of players were informed, the German Football Federation (DFB) confirmed on Sunday.
After a 30-minute suspension due to thunderstorms in the first half, the game continued as normal. Before kick-off for the second half, referee Michael Oliver could be seen talking to captains Ilkay Gündogan und Kasper Schmeichel and looking up.
Spectators and TV viewers assumed they were looking at the sky to see if another thunderstorm was coming but they were actually looking at the roof to see if they could spot the man, after Oliver had been informed by UEFA officials.
It was decided to carry on with the game and the players did not seem distracted.
The incident raises further questions about security at Euro 2024, where fans have already entered the pitch on several occasions without permission.
On Sunday, tournament organizer UEFA said it had no comment and referred dpa to the police statements.