The court heard Sharp had a string of previous convictions for sexual offences, beginning when he was just 16 and he harboured perverted sexual fantasies involving the gagging, raping and murdering of women - which he acted out on Miss Gowing.
And just hours before the murder he left another woman tied to a bed after she refused to take part in perverted sexual acts, Mold Crown Court heard.
You are, on any view, a very serious danger to women.
The judge said Sharp broke into Miss Gowing's house in the middle of the night, tied her to the bed and kept her prisoner while she was raped repeatedly and sexually abused.
Then, in a further "callous act", he cut up her body and disposed of her in various places along the River Dee.
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It comes as 22 charities signed an open letter vowing to improve safeguarding, and apologising for 'failures' in the sector.