A retired teacher knocked his wife out with a dumbbell and then slit her throat in a 'mercy killing ' at their £390,000 home because he could n't cope with her dementia , a court heard . John Colin Bennett , 75 , killed his wife Beatrice , 75 , at their North Shropshire home after struggling to come to terms with her debilitating condition . His devoted wife of 55 years had been left unable to recognise her husband as a result of Alzheimer 's disease and regularly called him a 'double ' or an 'imposter ' . John Colin Bennett , 75 , killed his wife Beatrice , 75 , at their £390,000 North Shropshire home ( pictured ) In May last year Mr Bennett decided he wanted to 'end her pain ' and severely struck his wife with several blows to the head with a dumbbell fracturing her skull . He then cut her throat with a kitchen knife before calmly calling 999 and telling operators : ' I 've done a terrible thing , I have murdered my wife . ' The pensioner was detained in a psychiatric clinic under the Mental Health Act yesterday after previously admitting manslaughter at Stafford Crown Court . Judge Simon Tonking said : 'This was n't a premeditated killing . It was , in part , an act which you believed to be one of mercy . ' The court was told the happily married couple , both retired teachers , were completely devoted to one another but were unable to have children . They were described as a very 'private couple ' who lived in Market Drayton , Shropshire , and relied on one another for almost everything . He then cut her throat with a kitchen knife before calmly calling 999 and telling operators : ' I 've done a terrible thing , I have murdered my wife ' The pair had a 'happy and active ' retirement until Mrs Bennett , known as Trixi , began to show signs of dementia in 2011 . Prosecutor Deborah Gould said : 'She was an enthusiastic bridge player and her condition first became noticeable whilst she was playing . 'Mr Bennett became plagued with fears about their future , he became depressed , unable to sleep and was on sleeping tablets . 'What undermined the world of this couple was age . ' When he dialled 999 to hand himself in , he said : 'She has Alzheimer 's . I hit her on the head to stun her . ' I could n't see her suffer any more so I put an end to it . 'She did n't recognise me as her husband . I have had two years living with this stress . ' Michael Duck QC , for the defence , said : 'That which emerges most strikingly is the depth of affection between husband and wife , the way they had supported each other as individuals for five and a half decades . 'On any view , a happy married life . He is contrite in the extreme . The pressures brought to bear on that particular day came together in a tragic few moments . ' Speaking at the time of the death neighbours of the couple in the picturesque market town expressed shock at the news . Local resident Paul Dawson , 48 , said : 'Trixie was very ill . I ca n't believe it was murder , he was probably trying to help her die . 'It 's just not possible , somewhere like this . I 'm just gob-smacked . ' Another neighbour James Mullineaux , 68 , a retired police officer , added : 'They were a well respected elderly couple just enjoying their lives together . '
John Colin Bennett , 75 , killed his wife Beatrice , 75 , at their £390,000 home . Retired teacher was struggling to cope with her dementia and care for her . He knocked wife out with a dumbbell and slit her throat in a 'mercy killing ' Mr Bennett then calmly called police and said : ' I have murdered my wife ' He has been detained in a psychiatric clinic under the Mental Health Act .