In Australia, police interview and question; they do not interrogate. The reason is that police are seeking to find the truth, or facts, that they then used to decide if an offence has been committed and if charges should be laid. Often, in serious matters and if an investigation has occurred, police alone will not decide whether to charge but the decision may be made by the Director of Public Prosecutions, after having received and reviewed a brief of evidence compiled by police.
The procedures involved to get to the point of a person being charged are bewildering - even to legal practitioners.
For an interview to be accepted in court, the person being interviewed must be "competent". That can mean many things, ranging form being sober and not affected by alcohol, not affected by drugs, not experiencing a mental episode, such as being delusional, not overly tired (so interviews can't go on for such a long time the person becomes exhausted and mentally confused - or could be thought so), be able to understand the questions, either because they have limited or no English - and so need an interpreter; or are of low intelligence or other intellectual impairment and would by that impairment be unable follow questions. Aboriginal Australians and immigrants from contries where police and security services are thugs, can also feel intimidated and fearful; hence special provisions for interviews are made for those cases too. Police can't refuse water and food or toilet breaks, so as to induce stress, or anxiety or humiliation. A person can't be prevented from using the toilet in the hope that shame at soiling themselves will induce a "confession".
The aim of the interview is for police to elicit information from the interviewee voluntarily and which is not coerced; and with the interviewee fully aware they are not required to say anything. If courts can be convinced the interview was coerced or the interviewee was in some way forced or coerced into providing information or admissions, the information may be excluded and can't be used in the prosecution. It seems that Mr Lynn's defence team are going to attempt to do this at least for some of the evidence.
One possible line the defence may take - and this is speculation - is that if police believed Mr Lynn was contemplating or intending self harm (and they have admitted they did and this prompted Mr Lynn's arrest) then the conclusion may be drawn that Mr Lynn was in a mental state so fragile that rendered him unfit for interview and that any admissions he made are for that reason inadmissible and can't be used by the prosecution.
We do not know if a doctor or psychologist saw Mr Lynn post arrest and gave a professional opinion that he was in a fit state for interview. If that occurred, that would strengthen the Crown's case that the interviews Mr Lynn gave were conducted in accordance with accepted practices and norms and the information elicited was not coerced or given when he was not fit to do so.
The other reason there appears to have been several interviews over several days is that police have to make a transcript of the interview, review them and decide what questions they will ask. There was an enormous amount of territory that would have been covered. It is likely police would begin when he left his home to travel to the valley, what was he driving, wearing, why was he carrying firearms and a knife, and so on. It would also include such things as if he bought fuel (and where), what route did he take into the valley, what did he do and his movements there, prior to the fateful day. This sets the scene. It gives interviewers a "base line" on how Mr Lynn replies to innocuous questions, the style of language, and the extent of his recollections and their accuracy. He may have made admissions immediately; we do not know. Police will likely "drip feed" information to him, to let him know they have been tracking him for years and also use the technical and witness information first, before the listening devices. But precisely what the police interviewers do - and they receive extensive training - will be determined by My Lynn's answers, his demeanour and so forth.
In short, the interviews that occur are nothing like the interviews we see on Law and Order or so American program.
Police interviews are seldom released in Australia. If you want to see how Canadian police conduct an interview, have a look at this:
. It is basically the same method used here.