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A controversial art exhibition in Manhattan has people asking: Can a weapon be art?

"A Knock at the Door" features stamps depicting a gun to President Bush's head, a straightjacket made from an American flag and what appears to be a suitcase bomb ( search). The artists have received mixed reviews from both the art police and the real police — a few have been questioned, detained and even charged with crimes related to their work.

Even those who support the exhibit have questions about some of its displays.

• Click in the video box to the right to watch a report by FOX News' Jamie Colby.

"What is provocative and what is safe and free?" asked Tom Healy, president of the Lower Manhattan Cultural Council ( search). "I don't have the answer to that in these particular works. And it's not a surprise that authorities would be interested in some of these things. They're works that are pretty hard not to find offensive."

And that's the point of the exhibit — not to provide answers but to ask visitors to decide what is offensive and what is art.

For some relatives of Sept. 11, 2001 ( search), victims, one answer is clear.

"From our point of view, and I think from a lot of Americans' point of view, it's a slap in the face," said Michael Burke, who lost his brother in the terrorist attacks four years ago. "It's meant to appeal to those who agree with it and they look at it and they chuckle, and everyone else it's meant to be offensive to."

The LMCC says it sensitive to the issues surrounding Sept. 11. One of its studios overlooks Ground Zero, where the council lost its office — and one of its artists — in the attacks.

But it's hard for many not to get the shivers after looking at the suitcase bomb, especially with the artist, Chris Hackett, facing firearms charges after the discovery of a weapons cache in his studio when police responded to an explosion caused by one of his other projects.

Organizers assure no explosions here — but the exhibit may bomb.

Click in the video box above to watch a report by FOX News' Jamie Colby.