Art experts said on Monday, that there was an astounding haul from Boston's Gardner Museum -- possibly the biggest art theft in US history.
The sentence is about the the act of someone taking possession of some item from the Boston's Gardner Museum.
( z1 concern :ARG0 ( z2 sentence ) :ARG1 ( z3 act :ARG0 ( z4 someone :ARG0-of ( z5 possess :ARG1 ( z6 item :mod ( z7 some ) :source ( z8 museum :name ( z9 name :op "Gardner" :op "Museum" ) :location ( z10 city :name ( z11 name :op "Boston" ) ) ) ) ) ) ) )