Doherty had a three-year-affair with mum-of-two Ms Harrison, who lived in Highbury, North London, before she went missing after a shopping trip before a planned holiday to Florida.
He consistently denied murdering his lover but was jailed for 12 years at the start of 2013.
Now Doherty, from South London, is set to be freed next November after serving half of his original sentence.
Ms Harrison’s devastated family have blasted the decision to free Doherty, calling it a “shambles”.
Her sister Maxine told the Islington Gazette: “He’s destroyed the lot of us – it’s a disgrace. Every day we are no nearer to finding Jane.
She added: “Where has the British justice gone? My mum and dad have died now – gone to the grave without knowing what happened. Me and my sister are still fighting it.”
The prosecution stated that Doherty killed his lover before taking her body to a lock-up garage and reporting her missing the following day.
He was questioned about her abduction in 1995 but was arrested after a murder inquiry was launched in 2012.