Initially the victims were shot by the Einsatzgruppen and others; gas chambers and gas vans using carbon monoxide were used by early 1940.[307][308] Under the Law for the Prevention of Hereditarily Diseased Offspring, enacted on 14 July 1933, over 400,000 individuals underwent compulsory sterilisation.[309] Over half were those considered mentally deficient, which included not only people who scored poorly on intelligence tests, but those who deviated from expected standards of behaviour regarding thrift, sexual behaviour, and cleanliness.