A Zumba instructor accused of killing his girlfriend and possibly dumping her body in a suburban Brisbane tip told detectives "I didn't do it" during his police interview — moments after being shown photos of authorities excavating his front yard.

Mark Sheridan Waden, 44, is facing a Supreme Court trial over the alleged murder of Priscilla Brooten, a US citizen who disappeared in 2018 from the Brisbane home they shared. Her body has never been found. Waden has pleaded not guilty.

On Wednesday, the jury watched a 90-minute police interview from June 2019. In it, Waden detailed how his relationship with Brooten soured after he started a new job in real estate, working long hours and having less time for a social life. He also blamed Brooten's mental health.

He told police the situation got worse when he discovered she'd been in Australia illegally, and he feared the legal consequences. "Finding out about her past, her aliases, different surnames, she wasn't a nice person," he said. Waden claimed Brooten had been using him to stay in the country, spending his money while also relying financially on her ex-boyfriend, Steve Thompson.

Waden described Brooten as "very secretive" about her laptop and said she had a "very closed" life, refusing to talk about her past. He told police that one day in 2018, he returned home to find Brooten had left, taking about three suitcases worth of clothing. He said he assumed this was because he'd told her he wanted to end the relationship and had threatened to call immigration on her.

The jury has heard that Waden allegedly factory reset Brooten's phone after her disappearance and gave the device to his new girlfriend, Desiree Hatzipapas. Waden told police he started dating Hatzipapas around the time his relationship with Brooten broke down. The court earlier heard Brooten had discovered messages between the pair.

Throughout the interview, Waden expressed concern about picking up Hatzipapas from the airport. Towards the end, he was told police were excavating his yard and shown photos of the scene.

"Considering my yard is being dug up and whatever else has been happening in my house, I think I'd like a lawyer or solicitor present, considering where this direction is heading now," he said.

When asked if he understood he was under arrest for Brooten's possible murder, Waden said: "Yeah, I didn't do it."

Earlier, police asked if he organised to drive Brooten's Volkswagen Golf to Scarborough, where her ex-boyfriend lived. Waden said no. Detective Anthea Johnston then pressed him: "So, you're telling us that she left the phone at your house, pin locked, then you give that phone to Desiree?"

Waden answered: "I reset the phone. You enter … an incorrect code like, I got online, and I looked and she entered the code like 10 times and it factory resets the phone."

Asked why he'd do that if it was Brooten's phone, he said she never collected it and he assumed she left it because he threatened to call immigration. He also said he believed she left the phone because it could be tracked by the SIM card.

Waden admitted he'd restrained Brooten in a bear hug and slapped her once. He told police that on the day she disappeared, he had his first listing as a real estate agent at Bees Nees Realty in late June 2018. He said Brooten knew it was important, but they were arguing so heatedly that he pulled over at the Milton McDonald's in Brisbane and told his boss he wouldn't make the listing. He admitted lying to his boss, saying he was with police that day because he didn't want to lose his job.

He also told police he lied to Hatzipapas about aspects of his relationship with Brooten because Brooten was still living with him and he didn't want to ruin something new.

The trial continues.