"I went on a date with Grace Millane's killer." 20 minutes in, Kate's instincts told her something was off.

This post deals with murder and includes violent details that might be triggering for some readers.

Kate* met Grace Millane’s killer on Tinder while her body still lay in his apartment.

She had no idea the guy opposite her sipping on his beer on a Sunday afternoon had strangled the British backpacker the night before – but it didn’t take long for her to realise she was unnerved by him.

Writing for Newshub, the anonymous author, who we’re calling Kate, wants to warn women to always “trust your instincts”.

Watch: New Zealand Prime Minister Jacinda Ardern’s message to Grace’s family. Post continues after video.

Grace Millane’s killer was found guilty last month of murdering the 21-year-old in December 2018, hiding her body in a suitcase and dumping it in bushland outside Auckland, New Zealand. Her body wasn’t found until eight days after their date.

Kate thinks she’s the first person this man, who cannot be named for legal reasons, had a proper conversation with after he committed the unspeakable act.

Their conversation started like any average Tinder date, talking about what they’d done that day. He’d been shopping for a suitcase with wheels or a bag with wheels. He was worried he couldn’t find one that was big enough for his sport gear.

“It makes me quite sick now to think of what that suitcase was actually used for,” she writes.

Kate could tell right away he was aloof, that he wasn’t there for her or a connection. He also drank his first beer super fast – which she found off-putting. It was the first real sign to her that something was off.

He told her his friends were all policemen. He mentioned they’d been having a hard time recently with police dogs trying to find bodies. “They can’t smell deeper than four feet,” he remarked.

Little did she know, he hadn’t buried his victim yet. He’d do that the next day.

Kate tried to keep up with the conversational theme of crime. She told him she was a journalist and had watched a man being put away for murder.

"It's funny how guys make one wrong move and go to jail for the rest of their lives," he responded.

He then talked about some guy he knew whose partner asked to have rough sex and who ended up dying from suffocation. "It was really tough for him to see this woman he loved dying," he said.

Little did Kate know, this would become his story - his attempt at an alibi later in court. But even though at this point it was still just an unsettling story she was being told on a date, Kate felt uncomfortable.

When she got up to get water from the bar, she was careful not to leave her drink behind.

"For some reason, I felt like he was the type of guy who would spike it. I felt bad for thinking that though," she writes for Newshub.

After an hour and a half, they decided to part ways. Kate had stuck around to be nice, she didn't want to be rude and up and leave after 20 minutes like she wanted to. Even though now she wishes she had.

He told her his car was down the very street where she parked, so she lied and said hers was in the opposite direction.

In hindsight, Kate thinks he was using the date to test alibis on her and to process what he'd done. She only wishes he'd spilled more evidence that she could have later leaned on in court.

After their date, the 27-year-old hired a carpet cleaning machine and bundled Grace's body into a rental car that he'd drive out to the Waitakere Ranges the next morning.

Kate wants anyone who reads her words to listen to their instincts. Especially when they're as strong as hers were.

"Lies are easy to spot too. If it doesn’t add up or seems to be too good to be true, it likely is," she writes.

It took a jury of seven women and five men five hours to unanimously agree on a guilty verdict for Grace's killer.

He showed no emotion as the verdict was read out, but has to wait until February to be told how long he'll spend behind bars.

Kate's story is an important message for all of us. To always trust your instincts.

Read Kate's full story on Newshub. 

*Kate is a name chosen by Mamamia to represent the author who has decided to remain anonymous in telling her story via Newshub. 

Feature image: Facebook. 

If this post brings up any issues for you, or if you just feel like you need to speak to someone, please call 1800 RESPECT (1800 737 732) – the national sexual assault, domestic and family violence counselling service. It doesn’t matter where you live, they will take your call and, if need be, refer you to a service closer to home.