Investigators said they believe the thief entered the home through an unlocked side door Aug. 23 while the maid was out and the owners were in a back room, the Los Angles Times reported Tuesday.

At least a dozen paintings -- including works by Marc Chagall, Diego Rivera, Hans Hofmann, Chaim Soutine, Arshile Gorky, Emil Nolde, Lyonel Feininger and Kess van Dongen -- were stolen from the home, said Detective Donald Hrycyk of the Los Angeles Police's art theft detail.

"Somebody did this very quickly," Hrycyk said.

Hrycyk said the thief or thieves will likely find the artworks difficult to sell as they have all been reported stolen in New York's Art Loss Register, as well as FBI and Interpol stolen art files.