Actually.... if you read what he wrote... he said (oddly enought) "stolen / disappeared" why would he use the word "disappeared....." I'll let you answer that one.
Mark Karpeles said in sworn declarations: "On February 24, 2014, MtGox suspended all trading after internal investigations discovered a loss of 744,408 bitcoins presumably from this method of theft." By "method" he is referring to transaction malleability.
Source:
http://www.scribd.com/doc/212477228/Karpeles-Declaration