Police said a 32-year-old man is now being held under the Mental Health Act.
It follows the death of Margaret Evans, 69, whose body was found at her home in Knockancor Drive, Portstewart, last week.
She had been beaten. Mrs Evans was well known in the town where she ran a hair salon before stepping down in January.
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The son of a woman found dead at her County Londonderry home has been released from police custody.