While in his flat, Lau estimated that he struck the teenager with a ketchup bottle more than 10 times, as he bound her limbs, neck and head with ties and adhesive tape.

Bodily fluids found on dead teen may belong to murder suspect, court told

Lau also assaulted her private parts with a bottle of Chinese wine, before forcing the remaining alcohol down her throat, he told police officers who interviewed him after the alleged murder.

“The anger [I have] for the world and company was projected on to her,” he told officers, adding that his former colleagues used to mistreat him and teased him for being short.

Lau, 37, denies murdering Kwok, who he knew as “Siu B” – the name she used in the phone application through which they communicated.

Footage of investigators interviewing Lau after his arrest was played to the jury of seven in court on Friday with the accused – who mostly appeared calm in the video but at times became emotional – providing a detailed and graphic account of the alleged murder.

Lau became emotional recounting the night of the alleged murder. His wife had talked to him – and he felt as though they were about to be “parted by life and death”.

But he remained largely calm when he explained to the investigators during the interview why he forced himself on to the girl in the hotel, despite believing she was already dead.

“It has got to this point anyway. Don’t let it be wasted,” he told officers, before quickly withdrawing his comment. “But it should not be put like that.”

Lau said he met Siu B over a phone app and had been exchanging information on another messenger app, WeChat, about a private photo shoot he would pay her HK$500 (US$64) for on December 8.

But when they arrived at Lau’s flat at Kam Fong Street, she mentioned her work. “I started to talk about my scar,” he said, which reminded him of old office politics and his ex-colleagues.

Lau, a former logistic worker, then began hitting her with a ketchup bottle. He said he put plastic ties on her hands, but they were not effective as she resisted. “Probably the ties are not for that purpose,” he said.

He eventually placed her hands in front of her head and wrapped them together with adhesive tape, making her unable to move her upper body.

Lau said he then sexually assaulted her with a Chinese wine bottle. He then forced the rest of the wine – 250 millilitres, he estimated – down her throat.

He recalled that at one point Kwok, after being hit repeatedly with the bottle, said she would succumb.

But fearing his wife and mother-in-law’s return was imminent, he thought: “The time has come. This is the only way to make [her] stop moving.”

Lau then wrapped three ties around her neck – during which she struggled the most, he said – before her breathing slowed and her heart stopped beating.

Girl tied up, assaulted and murdered after refusing to wear costume during photo shoot, court hears

But Lau claimed he was still not sure whether she was dead. “I am not a professional,” he said. He was only certain the next day when he returned to the Harbour Hotel, where he hid her, and found a “smell” in the room and rigor mortis on her body.

The events at his home lasted for less than half an hour, Lau said, before he wheeled Kwok in a suitcase to the hotel. There, he had intercourse with her twice, he said.

Lau said he left the girl in the hotel for the night and returned home. He went back the following morning to dispose of her body in a nylon bag and hand cart at a rubbish station three blocks away.

“I [had been thinking] it had all passed and whether there was still a chance for me to become a good person again,” he told officers during the interview.

But police caught him at home in the afternoon after he had disposed of the body. “I wondered whether it was payback time,” he said, bursting into tears.

“I want to pay back big time, not in a minor fashion,” he said, before pledging to help the police.

He told the officers he deserved to be caught and that he would accept what he had done.

Lau said he put the ketchup bottle back in the fridge because “there was still some left”. He gave Kwok’s jacket to a homeless person. He gave away hair conditioner he took from the hotel in his neighbourhood.

The defendant showed little emotion on Friday as he revisited what he said during the police interview.

It was revealed in court on Thursday that he was taking medication for mental illness.

The trial continues before Mr Justice Kevin Zervos on Tuesday.