By . Sophie Jane Evans . and Lizzie Parry . PUBLISHED: . 07:29 EST, 18 December 2013 . | . UPDATED: . 09:11 EST, 2 January 2014 . Guilty: Nathaniel Flynn is facing life in jail after admitting murdering his 84-year-old grandmother and trying to kill a nine-year-old boy . A cannabis user who murdered his 84-year-old grandmother, stabbing her 50 times as she lay in her bed, and then attempted to kill a nine-year-old boy, has been sentenced to life in prison. A judge today told Nathaniel Flynn, 27, that he will face at least 24 years behind bars as he passed a life sentence at Bradford Crown Court. Mr Justice Keith said the most likely explanation for why he killed retired teacher Louisa Denby was that 'she just got on your nerves'. Flynn admitted killing Ms Denby at their home in Shipley, West Yorkshire, in July, and stabbing Jason D’Arcy in a nearby skate park later the same day. The court heard that Jason suffered a shallow wound to his chest and a much more serious injury to his arm as he tried to defend himself. The judge heard that three psychiatrists found he had no diagnosable mental illness but said he had been influenced by his heavy, 'entrenched' use of cannabis and other drugs. Speaking after Flynn pleaded guilty earlier this month, police officers said they had no idea what drove Flynn to commit the 'brutal and frenzied' attacks. Julian Briggs, from CPS Yorkshire and . Humberside’s Complex Casework Unit, said: 'This defendant is responsible . for two vicious and unprovoked attacks. 'It has not been possible to establish what drove Flynn to commit these awful crimes. 'He . has now admitted his responsibility and pleaded guilty to charges of . murder and attempted murder. 'We hope this brings some measure of comfort . to the families of both victims.' Flynn, . from Shipley, was due to go on trial two weeks ago, but admitted the . charges at Bradford Crown Court on December 3. Flanked by four prison officers in the dock, he wore a . blue shirt and jeans and was joined by members of his family. He showed no emotion as he confessed to murdering his grandmother, before stabbing the terrified schoolboy who had been playing nearby. Murder: Louisa Denby, 84, left, was stabbed to death by her grandson, right, at their shared home in Shipley . Scene: The 'brutal and frenzied' attack took place at Ms Denby's home in Shipley, West Yorkshire (above) Sentencing: Left, Lee D'arcy, father of nine-year-old Jason D'arcy, who Flynn tried to murder, outside court. And right, Barbara Robinson, the daughter of Louisa Denby was in court to hear the sentencing . Speaking after the hearing on December 3, Detective Chief Inspector Nick Wallen, of West Yorkshire Police, . said: 'Louisa Denby was subjected to a brutal and frenzied attack at the . hands of her grandson Nathanial Flynn. 'To this day we still have no idea why he attacked her. 'Louisa was a lady, adored by her family, who had only ever shown her grandson love and kindness. 'Having murdered his grandmother, Flynn then targetted and attacked a young boy as he played in a skateboard park. Investigation: A police handout of CCTV showing Nathaniel Flynn at a local convenience store issued by West Yorkshire Police . Attempted murder: Flynn then tried to kill a nine-year-old schoolboy as he played at a local skate park (above) Standing guard: A policeman stands at the skate park where the boy was stabbed in the arm by Flynn . 'He was stabbed through the arm and it was only through sheer luck that he wasn’t murdered by Nathanial Flynn on that day. 'On . behalf of West Yorkshire Police I would like to pay tribute to the . people of Shipley who assisted the police to quickly detain and arrest . Nathanial Flynn. 'I would also like to thank all of those members of the local community who provided the police with witness statements.' Horrific: Today, police said they had no idea what drove Flynn to commit the violent attacks . Case: The 26-year-old is due to be sentenced at Bradford Crown Court, pictured, on December 18 . Flynn also faced two other charges, which will remain on file, the court heard. It is believed his mother, who lives in America, was due to fly to the UK to attend his sentencing  today. The schoolboy's father is also expected to be present. Addressing Flynn on December 3, Mr Justice Keith said: 'There is only one sentence I can pass and that is a sentence of life imprisonment.'
Nathaniel Flynn, 26, stabbed to death his grandmother Louisa Denby .
He then tried to kill a nine-year-old boy at nearby skate park in Shipley .
Judge hands Flynn a life sentence adding he will serve at least 24 years .
By . Sophie Jane Evans . and Lizzie Parry . PUBLISHED: . 07:29 EST, 18 December 2013 . | . UPDATED: . 09:11 EST, 2 January 2014 . Guilty: Nathaniel Flynn is facing life in jail after admitting murdering his 84-year-old grandmother and trying to kill a nine-year-old boy . A cannabis user who murdered his 84-year-old grandmother, stabbing her 50 times as she lay in her bed, and then attempted to kill a nine-year-old boy, has been sentenced to life in prison. A judge today told Nathaniel Flynn, 27, that he will face at least 24 years behind bars as he passed a life sentence at Bradford Crown Court. Mr Justice Keith said the most likely explanation for why he killed retired teacher Louisa Denby was that 'she just got on your nerves'. Flynn admitted killing Ms Denby at their home in Shipley, West Yorkshire, in July, and stabbing Jason D’Arcy in a nearby skate park later the same day. The court heard that Jason suffered a shallow wound to his chest and a much more serious injury to his arm as he tried to defend himself. The judge heard that three psychiatrists found he had no diagnosable mental illness but said he had been influenced by his heavy, 'entrenched' use of cannabis and other drugs. Speaking after Flynn pleaded guilty earlier this month, police officers said they had no idea what drove Flynn to commit the 'brutal and frenzied' attacks. Julian Briggs, from CPS Yorkshire and . Humberside’s Complex Casework Unit, said: 'This defendant is responsible . for two vicious and unprovoked attacks. 'It has not been possible to establish what drove Flynn to commit these awful crimes. 'He . has now admitted his responsibility and pleaded guilty to charges of . murder and attempted murder. 'We hope this brings some measure of comfort . to the families of both victims.' Flynn, . from Shipley, was due to go on trial two weeks ago, but admitted the . charges at Bradford Crown Court on December 3. Flanked by four prison officers in the dock, he wore a . blue shirt and jeans and was joined by members of his family. He showed no emotion as he confessed to murdering his grandmother, before stabbing the terrified schoolboy who had been playing nearby. Murder: Louisa Denby, 84, left, was stabbed to death by her grandson, right, at their shared home in Shipley . Scene: The 'brutal and frenzied' attack took place at Ms Denby's home in Shipley, West Yorkshire (above) Sentencing: Left, Lee D'arcy, father of nine-year-old Jason D'arcy, who Flynn tried to murder, outside court. And right, Barbara Robinson, the daughter of Louisa Denby was in court to hear the sentencing . Speaking after the hearing on December 3, Detective Chief Inspector Nick Wallen, of West Yorkshire Police, . said: 'Louisa Denby was subjected to a brutal and frenzied attack at the . hands of her grandson Nathanial Flynn. 'To this day we still have no idea why he attacked her. 'Louisa was a lady, adored by her family, who had only ever shown her grandson love and kindness. 'Having murdered his grandmother, Flynn then targetted and attacked a young boy as he played in a skateboard park. Investigation: A police handout of CCTV showing Nathaniel Flynn at a local convenience store issued by West Yorkshire Police . Attempted murder: Flynn then tried to kill a nine-year-old schoolboy as he played at a local skate park (above) Standing guard: A policeman stands at the skate park where the boy was stabbed in the arm by Flynn . 'He was stabbed through the arm and it was only through sheer luck that he wasn’t murdered by Nathanial Flynn on that day. 'On . behalf of West Yorkshire Police I would like to pay tribute to the . people of Shipley who assisted the police to quickly detain and arrest . Nathanial Flynn. 'I would also like to thank all of those members of the local community who provided the police with witness statements.' Horrific: Today, police said they had no idea what drove Flynn to commit the violent attacks . Case: The 26-year-old is due to be sentenced at Bradford Crown Court, pictured, on December 18 . Flynn also faced two other charges, which will remain on file, the court heard. It is believed his mother, who lives in America, was due to fly to the UK to attend his sentencing  today. The schoolboy's father is also expected to be present. Addressing Flynn on December 3, Mr Justice Keith said: 'There is only one sentence I can pass and that is a sentence of life imprisonment.'
that he will face at least 24 years behind bars as he passed a life sentence at Bradford Crown stabbing Jason D’Arcy in a nearby skate park confessed to murdering his grandmother, before was stabbed to death by her grandson, right, at murder: Flynn then tried to kill a nine-year-old