Complex sentence: Mary Ann Cotton (born Mary Ann Robson in October 1832 in Low Moorsley, County Durham--died 24 March 1873) was an English woman convicted of murdering her children and believed to have murdered up to 21 people, mainly by arsenic poisoning.
Split into simpler sentences: Mary Ann Cotton (born Mary Ann Robson; October 1832--24 March 1873) was an English woman convicted of murdering her children. She was believed to have murdered up to 21 people, mainly by arsenic poisoning.