After reading through some of the thread, I think there could be a lack of understanding about the law enforcement process.
Investigation
AFAIK, the interview process of the accused does not consist of just 1 or 2 questions, i.e. (a) Are you guilty of the offence or (b) Why did you do it? The interviewer (investigator or IO) would start off by asking the routine/ administrative questions, e.g. a line of questioning could be as follows:
1. Did you go to school this morning?
2. What time did you leave home?
3. How did you get to school?
4. Did you take a detour?
{If the accused is not truthful, investigator will introduce evidence to counter him}
E.g. Since you said you didn't make a detour, why does the CCTV show that you went to XXX block?
5. Etc.
In other words, the IO would have prepared his questions and evidence. If the accused is not truthful, most of the time, the IO would have been able to detect inconsistencies in the statement and try to probe further. If the accused is innocent and refuse to even answer simple questions, it makes the IO rather suspicious.
The police does not need an admission of guilt from the accused to press charges. As long as there is sufficient evidence to prove the case beyond reasonable doubt, the IO will make a recommendation to charge the accused. As far as I can tell, the likelihood of false convictions are very low in Singapore, the higher probability is that the accused is set free from of lack of evidence.
Formal Charge
After the decision to press charges has been taken, the accused will be formally informed of the charge(s). A cautioned statement in the following manner would be taken:
“You have been charged with [or informed that you may be prosecuted for] —
(set out the charge).
Do you want to say anything about the charge that was just read to you? If you keep quiet now about any fact or matter in your defence and you reveal this fact or matter in your defence only at your trial, the judge may be less likely to believe you. This may have a bad effect on your case in court. Therefore it may be better for you to mention such fact or matter now. If you wish to do so, what you say will be written down, read back to you for any mistakes to be corrected and then signed by you.”.
Whether the accused remained silent or say something, it will be recorded down.
Trial
Only after the above, will the accused by presented in open court. Even at that moment, the accused can still ask for an adjournment, e.g. need time to appoint a lawyer.
As far as I know, usually there is a long lead time from investigation to trial, depending on complexity of case, might be months or years. There are also plea bargaining, representations to be made by defence counsel, pre-trial conference, etc.