The first murder of the year happened just a few hours into 2020, when Isaiah Usen-Satchell was stabbed to death close to his home in Norfolk Park.
Two men have been charged over his death.
Just a week later, two-year-old Keigan O’Brien died in Doncaster after being admitted to hospital in cardiac arrest.
A post mortem examination revealed the toddler had suffered head injuries.
His mum Sarah O’Brien, 32, and her boyfriend Martin Currie, 36, have been charged with murder.
The most recent death to trigger a murder probe was that of 39-year-old Leighton Owen, who was found dead in a flat in Hatfield House, Grove Place, Balby, Doncaster, shortly after 11pm on Wednesday, August 26.
Two women, aged 45 and 40, and a 21-year-old man, were arrested on suspicion of murder and later released under investigation as enquiries continue.
Anyone with information about any of the deaths should call South Yorkshire Police on 101 or Crimestoppers on 0800 555111.
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13. 14) Found injured
Stephen Riley, 43, was found injured in Darley Avenue, Athersley, on June 26 and died the following day. A 37-year-old man was arrested on suspicion of murder and a 41-year-old woman was held on suspicion of assisting an offender. Photo: Claire Lewis
14. 15) Found unconscious
Kimberley Smith, 35, was found unconscious in a property on Pavilion Way, Shiregreen, Sheffield, and died in hospital later that day. A 22-year-old man was arrested on suspicion of murder and bailed. Photo: Claire Lewis
15. 16) Stabbing
Simone Hancock, 55, was found stabbed to death at a flat in Ravenscroft Place, Richmond, Sheffield, on July 4. Kerry Taylor, 41, has been charged with murder. Photo: Claire Lewis
16. 17) Unexplained
Claire Anderson, 35, was found unconscious in a property on Thorne Road, Doncaster, on July 11 and died a short time later. A 38-year-old man arrested on suspicion of murder was released under investigation. Photo: Claire Lewis