1900 Born West Ham
1901 census living at 8, Nursery Lane, West Ham
1911 census living at 48 Herbert Road Manor Park E
1920 Apr 21. Died, suicide. age 20. Son of James C. and Mary Sibthorpe, of 48, Herbert Rd., Manor Park D Coy, 2nd Battalion.
"Blood on the Banner" says he was "shot dead at the British Army Barracks at the old jail in Ennis. The inquest into Private Sibthorpe's death returned a verdict of suicide but the press reports of evidence given by his comrades suggest foul play" I cannot find any press reports myself, but they could be in a Clare paper not available online.
Death in Irish GRO