On Sunday, masked men entered the National Portrait Gallery (NPG) in London, causing panic and a “stampede,” as the London Evening Standard reported. The intrusion occurred in the space devoted to BP Portrait Award 2015, an exhibition and international portrait painting competition sponsored by the oil company that awards each year’s winner £30,000 (~$46,300). The men were reportedly staging “a hoax heist in an apparent protest” against this partnership, which began in 1989.

Although they tried to remove an oil painting by Cleveland-based artist Frank Oriti from the gallery wall, the men fled empty-handed and were caught before they could leave the NPG. Witnesses describe two men “in balaclavas” as the main perpetrators, but police arrested four people in connection with the entire fiasco.

The museum described the event as an “isolated incident,” telling visitors that “no one was seriously hurt,” and it later issued the following statement:

The National Portrait Gallery can confirm that police were called to the Gallery at 15.33 on Sunday 5 July following an incident. Four men were later arrested in connection with the incident under the Public Order Act. The Gallery can confirm than none of its visitors or staff were physically harmed and nothing was stolen or vandalised. The incident is being investigated both by the police and internally, so the Gallery is unable to give out any further details at the current time.

This is not the first time BP and British cultural institutions have faced criticism and active backlash for such sponsorship deals. Artist and activist groups including Liberate Tate and Art Not Oil — both unaffiliated with Sunday’s incident — are pressuring museums to end these partnerships. While those groups have used visual art and performance to articulate their concerns, this most recent protest has received criticism not only for its proximity to the tenth anniversary of the London bombings, but also for its use of shock over substance.

“I have no problem with protests,” museum-goer John Birch told the London Evening Standard. “The arts have always danced with the devil for funding, but on the eve of the 7/7 anniversary to walk into a major tourist location wearing a mask is just utter lunacy. People were scared for their lives, and I thought there would be a shooting.”