A grandfather who murdered his wife and two grandchildren in central NSW has been charged with murder after he allegedly bashed his cellmate to death inside Sydney's Long Bay Correctional Centre. John Walsh, 77, was interviewed earlier on Tuesday morning over the fatal attack on convicted killer Frank Townsend, 71. Corrective services officers became aware of the assault about 10.50pm on Monday night. Officers found the 71-year-old inmate with serious head injures and rendered first aid.  He was transported to hospital where he later died.  Townsend was allegedly bashed to death by Walsh with a sandwich press, but a motive for the attack has not yet been established. The incident took place inside the Kevin Waller Unit for aged and frail inmates of the jail, located at Matraville in Sydney's south-east.  Walsh was detained by correctional officers before being arrested by police from Eastern Beaches Local Area Command and taken to Maroubra Police Station. Following inquiries by local detectives and the State Crime Command’s Homicide Squad, he was charged with murder and refused bail to appear at Parramatta Bail Court on Wednesday.  Walsh is serving life in prison for the June 2008 murders of his wife, Jean, 52, his seven-year-old grandson, Kevin, and his five-year-old granddaughter, Jaime. He bludgeoned his wife with a piece of wood and hammer and stabbed her in the neck, then battered Kevin to death and drowned Jamie in the bath inside their home at Cowra. The children's mother, policewoman Shelly Walsh, found the three after she returned from a court appearance at Parkes. She was admitted to hospital soon afterwards to undergo surgery for an axe wound. Townsend served time for manslaughter over the Wingham death of Belinda Trad. Ms Trad's body was found with several gunshot wounds at a house in July 2010. He was released in 2016 but had recently breached his parole conditions and had been taken back into custody