Criminal Liability for Unusual Art Forger?

According to this NYT article, Mark Landis has repeatedly forged artwork and presented it to museums as the real thing.  The tricky issue for legal scholars is that he donates his paintings:

Mr. Landis — often under his own name, though more recently as Father Scott or as a collector named Steven Gardiner — has indeed done a lot of traveling over the past two decades, but not for the church. He has been one of the most prolific forgers American museums have encountered in years, writing, calling and presenting himself at their doors, where he tells well-concocted stories about his family’s collection and donates small, expertly faked works, sometimes in honor of nonexistent relatives.

Unlike most forgers, he does not seem to be in it for the money, but for a kind of satisfaction at seeing his works accepted as authentic. He takes nothing more in return for them than an occasional lunch or a few tchotchkes from the gift shop. He turns down tax write-off forms, and it’s unclear whether he has broken any laws. But his activities have nonetheless cost museums, which have had to pay for analysis of the works, for research to figure out if more of his fakes are hiding in their collections and for legal advice. (The Hilliard said it discovered the forgery within hours, using a microscope to find a printed template beneath the paint.)

Does anyone want to take a stab at his criminal liability in the comments, assuming the allegations are true?  The article states that he received an "occasional lunch or a few tchotchkes," but you might also comment on his liability in cases where he received nothing at all.  For example, is this criminal mischief?