The case has retained its hold on the popular imagination, in part because known instances of serial murder were much rarer at the time than they are today. Jack the Ripper has provided themes for numerous literary and dramatic works. Perhaps the most notable was the horror novel The Lodger (1913; motion-picture versions, 1926, 1932, and 1944), by Marie Adelaide Lowndes (Lowndes, Marie Adelaide). More than 100 books about the case have been published, many of which offer conjectures as to the true identity of the murderer and the circumstances surrounding the crimes—including that the murders were part of an occult or Masonic plot and that the police were covering up for highly placed culprits, perhaps even members of the royal family. Many of these works, however, are based on fraudulent claims and documents. The most commonly cited suspects are Montague Druitt, a barrister and teacher with an interest in surgery who was said to be insane and who disappeared after the final murders and was later found dead; Michael Ostrog, a Russian criminal and physician who had been placed in an asylum because of his homicidal tendencies; and Aaron Kosminski, a Polish Jew and a resident of Whitechapel who was known to have a great animus toward women (particularly prostitutes) and who was hospitalized in an asylum several months after the last murder. Several notable Londoners of the era, such as the painter Walter Sickert (Sickert, Walter Richard) and the physician Sir William Gull (Gull, Sir William Withey, 1st Baronet), also have been subjects of such speculation. The murder sites have become the locus of a macabre tourist industry in London.