ADDED: Jules Crittenden has some doubt that it was Holocaust deniers:
[I]t could be neo-nazi enthusiasts who want it for their clubhouse. Could be someone who wants to sell it to a World War II memorabilia collector. Or, it could be scrap metal mongers. Turns out the thing is made of bronze. In the past couple of weeks, someone pried off a 100-year-old commemorative plaque at Lexington’s Battle Green, as well as a couple of plaques with the names of World War II and Vietnam war dead in Attleboro, Mass. Scrap metal thieves suspected. If it can be melted down, they don’t really care what it is.