Haines, a single father, returned home and told his fiancée, ‘I strangled someone.’ They are in Mill Pond.
Haines and the adolescent girl met at a local nightclub and were shown on CCTV calmly walking down the high street after leaving together in the early hours.
He was seen walking past Lily’s mother, who was waiting in her car to pick up her daughter.
‘What are you doing?’ exclaimed Lily’s friend as they exited the venue. You have a girlfriend… and she’s only 18!’
Haines and Sullivan kissed, cuddled and chatted in a secluded walkway but after an hour she ‘decided she was going home’, Swansea Crown Court was told.
In the court, the father-of-one admitted murdering Lily but insisted the attack was not sexually motivated, which would have lowered the sentencing threshold from 30 to 15 years.
His claims were thrown out after a hearing at the court revealed how the victim’s crop top was found on the bank of the water.
Shortly before 3am, Lily spoke to her mum on the phone, telling her: ‘I’ll be there now mam. I’m on my way. I’m a couple of minutes away. I’m nearly there.’ the court heard.
But the phone line died as Haines launched his attack, and CCTV footage showed Lily’s phone lighting up repeatedly as her mum tried to call her back 30 times.
Judge Thomas said: ‘I am sure Lily decided she was going home. Fuelled as he was by drink, I am sure Mr Haines was frustrated by this. He became forceful; she resisted.’
Haines claimed Lily had threatened to accuse him of rape, leading the judge to conclude that he lashed out as he ‘couldn’t risk her surviving’.
The court heard he had a ‘great deal to lose’ as he was also fighting a family court case to get access to his child.
Judge Thomas added: ‘He strangled Lily in order to prevent her telling people he had tried to get her to go further than she was willing.
‘His intention was to silence her. He didn’t want anyone to know what had happened in the lane.’
‘I am sure that Lily did not remove her own top voluntarily. I am sure that Mr Haines took it off her before he put her in the pond.
‘My firm view is that when he got forceful Lily did say that she would complain that he had tried to force himself upon her.’
Haines will be jailed for life in prison, with a minimum of 23 years