A man jailed for torturing and murdering his partner's two-year-old daughter has been killed in prison.
Subhan Anwar was convicted in February 2009 of murdering Sanam Navsarka, of Huddersfield, West Yorkshire, and given a minimum 23-year sentence.
He died on Thursday night at Long Lartin Prison in Worcestershire, the Ministry of Justice said. Two inmates were arrested on suspicion of murder.
Anwar is understood to have been held hostage in a cell before he was killed.
A West Mercia Police spokesman said: "West Mercia Police has launched a murder investigation after a 24-year-old man died in Long Lartin prison last night.
"The body of the man was found by prison officers just before 8pm on Thursday, February 14.
"Two men aged 47 and 45 have been arrested on suspicion of murder and are currently in police custody.
"West Mercia Police is working closely with the Ministry of Justice to establish the exact circumstances surrounding this man's death."
Anwar's partner Zahbeena Navsarka was cleared of her daughter's murder but found guilty of manslaughter and jailed for nine years.
Bradford Crown Court heard that the toddler suffered 107 injuries at Anwar's hands.
During a month-long ordeal a metal pole was used to shatter the child's leg. She died with fractures to all her limbs.
Sentencing the couple in 2009, Judge Peter Thornton QC said: "Your deliberate cruelty is beyond belief. Humanity has let her down."
The violence inflicted on the youngster happened near the end of her life.
Her hand prints and bloodstains were found inside cupboards where she had been put as a punishment at the home in Huddersfield and also at a property in Batley, West Yorkshire.
In January 2011, a social worker who failed to pass on vital information about Sanam's abuse just one week before she was murdered was suspended.
Judyth Kenworthy was warned that Sanam had a bruise on her head and had been locked in a cupboard but did not tell the child's assigned social worker or her own manager.
The General Social Care Council found Ms Kenworthy guilty of misconduct and suspended her from the social care register for two years.