A Hong Kong private tutor found guilty of orchestrating a failed plot to murder his business partner eight years ago has secured a three-year reduction to his 27-year jail sentence, but lost an appeal against his conviction.

In a written judgment on Friday, the Court of Appeal found that the sentence imposed on Stephen So Hon-to was too high, despite the egregious nature of the offence and the need to ensure a “continuing danger to society” would be removed from society for “a very considerable time”.

The court also explained its decision to dismiss So’s appeal against his conviction for conspiracy to murder and conspiracy to possess arms and ammunition without a licence last December.

It found the trial judge had correctly instructed the jury regarding So’s intention to commit a crime and the prosecutors’ burden of proof.

So, now 36, enlisted the help of three teenagers to kill former flight attendant Terence Lam Ching-fung between late 2018 and early 2019, after their relationship turned sour over a disagreement relating to an investment in a tactical gear company in mainland China.

The then 28-year-old tutor, a war game enthusiast, had also accused Lam, nicknamed “hobbit”, of secretly reporting to police that he had smuggled firearms.

A police investigation revealed he was in de facto control of three pistols, an assault rifle and 500 live rounds.

So first instructed his sexual partner, Chak Wing-sze, who was 17 at the time, to follow Lam and uncover his home address. He also left his guns and bullets in Chak’s care before putting his plan into action.

He first attempted to kill Lam on December 6, 2018, by luring his target into a derelict school in Tai Wo Hau, where he would be shot. The plan was cancelled after Chak forgot to prepare a mobile phone for her accomplice to use to call Lam.

So had distanced himself from the planned murder that night, giving instructions remotely while enjoying a fondue dinner with his girlfriend in Sha Tin.

Ahead of a second attempt to kill Lam on January 1, 2019, So took Chak to two abandoned village schools in Tai Po to test the firearms, and told her to buy explosive substances in case they decided to kill Lam with handmade bombs.

Police arrested So on New Year’s Eve in 2018 at the Hong Kong airport, just as he was about to depart for Japan with his girlfriend.

Court of Appeal justices Andrew Macrae, Kevin Zervos and Keith Yeung Kar-hung found the case was more serious than a murder plot in the making and was aggravated by the intended use of firearms and explosives and the creation of an alibi.

“It was the real thing, an egregious and intentionally murderous plan, masterminded and orchestrated by the 28-year-old applicant, who manipulated and used three young people, to kill and then dispose of the body of someone whom the applicant thought had wronged him, and him alone,” the judgment said.

The judges endorsed the trial court’s categorisation of the appellant as “a major threat to society”, but said his 27-year sentence for conspiracy to murder was “a very long sentence in respect of a crime that mercifully failed in its objective”.

“Although it is tempting to view such a sentence as richly deserving of condign punishment, given its purpose, its planning and the other aggravating features present, we consider that, in all the circumstances, it is too high,” the judgment said.

The appellate court reduced So’s 27-year sentence for conspiracy to murder to 24 years and upheld his 14-year term for the firearms offence, before ordering a concurrent sentence.

Factoring in a one-third discount granted to prisoners for good conduct, So would be eligible for early release in 2035 after serving 16 years behind bars.