Larissa Beilby died some time between June 22 and June 28, and was allegedly detained in a car against her will and tortured before she was killed, court documents reveal.

Detectives laid 18 additional charges — including torture — against the man accused of murdering Larissa, whose body was found in a barrel south of Brisbane on Wednesday.

The police bench charge alleged that "between the 22nd day of June 2018 and the 28th day of June 2018 at Buccan or elsewhere in the state of Queensland, one Zlatko Sikorsky tortured Larissa Laveen Beilby".

Mr Sikorsky was initially facing one count each of murder and misconduct with a corpse, but has since been charged with 18 other offences, including torture, deprivation of liberty, possessing weapons and dangerous drugs, and dangerous operation of a vehicle.

His case was briefly mentioned in the Maroochydore Magistrates Court on Monday morning, where he was remanded in custody until his next appearance in the Beenleigh Magistrates Court in September.

Outside court, lawyer Brendan Ryan maintained that Mr Sikorsky would fight the murder charge, but would not defend many of the other 19 charges police laid against him.

Sorry, this video has expired Lawyer Brendan Ryan speaks about new charges laid against Mr Sikorsky

"There are a lot of fresh allegations that the police have allowed me to see this morning, so all of those allegations in due course will be addressed," Mr Ryan said.

"There's a lot of fresh charges that have been brought against my client.

"A lot of those charges won't be defended. Police have located various items in the unit that he was located in so those charges will not be defended."

Mr Ryan on Sunday said Larissa died as a result of "misadventure" and will claim her death was not caused by drugs.

"Misadventure normally refers to circumstances relating to accident, so that's what misadventure means and that's what I'm going to stick with," he explained on Monday.

He expected police would deliver a "substantial part" of the brief of evidence against Mr Sikorsky in two months' time.

Mr Ryan would not say whether Mr Sikorsky was cooperating with police, but that he had spoken at length with police over a number of days and had not been formally interviewed.

Operation Quebec Jagger was launched after Larissa was found dead in the back of a ute in a gated community in Stapylton.

Mr Sikorsky was tracked to the Sunshine Coast and kept police at bay during a 27-hour standoff, eventually surrendering on Saturday night.

Detective Inspector Damien Hansen earlier confirmed Mr Sikorsky was in a relationship with the teenager, but would not discuss what could have motivated Mr Sikorsky to allegedly kill her.

Mr Sikorsky eventually surrendered on Saturday night after a 27-hour standoff. ( AAP: Darren England )

"I will say it's a very unique set of facts," Inspector Hansen said.

Scientific tests confirmed Larissa was the person found in a barrel at Buccan, but detectives are waiting on results to show a cause and time of death.

Larissa was last seen alive on June 15 at a halfway house for runaways in the Brisbane suburb of Sandgate. Police said she made a social media post three days later.

A 40-year-old Palmwoods woman, Tracey Ann Thomson, and 38-year-old Alexandra Headland man Joseph Geiger were also charged with one count each of accessory after the fact to murder.

Ms Thomson's case was also briefly mentioned in Maroochydore Magistrates Court this morning and she was remanded in custody until September.

Joseph Geiger faced court via videolink and complained to the court that he was due to start a new job on Monday.

A bail application for Mr Geiger was adjourned until Tuesday.

Police reveal details of siege

Superintendent Darryl Johnson said the police negotiators played a pivotal role in the siege ending safely.

Police gather outside the scene of the siege at Alexandra Heads on Saturday. ( AAP: Darren England )

"They were close enough to talk through the window … sometimes they're on the telephone, sometimes they're on a loud speaker," he said.

"In this situation, they were close enough to talk to the man."

Superintendent Johnson said officers did not storm in because they wanted to try to resolve it peacefully without risk to the person inside or to police.

He said at no stage was any other member of the public in danger, including people in units nearby.

"A decision was made to restrict people coming back into that area and we assisted people getting out if they needed to go to work," he said.

"There were quite a few situations where we took people back into their units to grab communications or clothes.

Police will allege Mr Sikorsky was in a relationship with the teenager. ( Facebook: Larissa Beilby )

"There were a number of people we did not allow back in and some were holidaymakers. I spoke to some myself on Saturday.

"Because we couldn't let them back into the unit, we sourced some extra accommodation to get them."

Superintendent Johnson said the siege ended "very peacefully … exactly how we wanted it to go".

"He [Sikorsky] walked out without any danger of being hurt," he said.

He said it was the second siege on the Sunshine Coast in the past few years but it was a "unique incident".

"The Sunshine Coast is a fairly safe place to live," he added.

