Actually the judiciary can direct the Police or AG to conduct further investigation or follow a line of query. This is not common but it does happen. The judiciary however cannot direct the investigation.
Here is a simple example. The accused testifies that at the material time that is stated in the charge sheet he was a guest of Obama at the White House and therefore could not be present at the Istana raping the chambermaid.
I can assure you that Judge will direct the DPP to inevestigate and the case will be stood down.
People will wonder why this was not established earlier but there have been cases especially old ones when people can't remember what they did years ago.
There was one case, where a girl who returned home late claimed that she was molested by an Ah Pek. She pointed out an Ah Pek at a Clementi Coffeeshop who was so blur that he had could not defend himself. During his trial, one of his friends remembered that he was in Changi Prison for another case. The case was adjourned for further investigation and it turned out that he was indeed serving time.
The judiciary has no say in the investigation process and requirement. It only deals with what's presented in court. At best (or worst, depending on POV), the judge can simply throw the case out of court for lack of evidence, but cannot tell the investigator and prosecutor or defence counsel what to look for and what to present.
