Armed police officers are positioned on the roof of the apartment block where Zlatko Sikorsky is holed-up, and residents have been warned the siege could go 'all night'.
Specialist police have been attempting to negotiate with the 34-year-old from his unit on Juan Street in Alexandra Headland on Queensland's Sunshine Coast since about 3pm.
Detectives looking for missing teen Larissa Beilby, 16, found a body now believed to be the teenager stuffed inside a barrel in the back of a ute, understood to have been dumped by Sikorsky near Brisbane on Wednesday.
Sikorsky's father, John, arrived on the scene wearing orange hi-vis to assist police with their efforts shortly after 9.10pm.
Queensland Police Superintendent Darryl Johnson confirmed Mr Sikorsky was helping police.
He exited the apartment complex almost two hours after he entered, appearing happy and animated as he spoke to police, before driving away in a Toyota Hilux.