Original: The police made a serious mistake by locking up over 20 alleged supporters of the Kelly gang between the third of January 1879 and 22 April 1879 under the Felons Apprehension Act 1878 .
Simplified: The police locked up over 20 possible supporters of the Kelly gang between January 1879 and April 1879 under the Felons Apprehension Act 1878 .