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Scottish police are looking for information about the pilot of a Greenpeace paraglider who flew an anti-Trump banner within 100 yards of the president.

Assistant Chief Constable Mark Williams of Scottish police told the BBC that the protestor had put themselves in “grave danger” by breaching a no-fly zone that had been established over the Trump Turnberry golf resort.

“On this occasion we could assess the situation and we realized there was no direct threat to the president, however it’s absolutely something that is very serious,” Williams said, adding that an investigation remains ongoing.

The aircraft carried a banner reading “Trump: Well Below Par” in protest of his his environmental and immigration policies, according to Greenpeace. The Associated Press reported the organization said it called in notice of the flight 10 minutes ahead of time.

Watch as @realDonaldTrump tries to hide from our message flying right over his head #resist #stoptrump pic.twitter.com/hINfBLpFoZ — Greenpeace UK (@GreenpeaceUK) July 13, 2018

The police search comes as an estimated 10,000 people took part in Edinburgh demonstrations against the president, and as others staged creative acts of protest just outside Trump’s resort. Scottish police have said 5,000 officers, at a cost to U.K. taxpayers of $6.6 million, could be involved in security for Trump’s golf weekend.