Under the Misuse of Drugs Act, the suspects might face the death penalty if more than 15g of diamorphine or pure heroin is trafficked.
The police say a number of handwritten letters, mobile phones, laptop, envelopes and hell notes were seized following their arrest.
Nirbhaya died in a Singapore hospital after 13 days of the rape, leaving millions in shock.
A 39-year-old suspect will be charged on Saturday under the Women's Charter, while investigations are going on for the other three suspects.
A recent study reveals that warm winds pouring down the sides of the mountain range are melting ice sheets up to 100 kilometres away.
The 64-year-old minister plans to return to Cambodia on May 7 to resume work as normal.
The Singapore Civil Defence Force (SCDF) is investigating the unnatural death and the cause of the fire.
According to the police, the two students bought plane tickets, got their boarding passes on April 30 but had no intention of leaving Singapore.
ICA and CNB says investigations related to the drug activities of all the arrested suspects are going on.
SIA authorities say that the latest initiative would provide the aviation industry with insight on the economics, logistical requirements and performance of biofuels.
Prince Harry is also scheduled to travel to Sydney to attend the events celebrating the Australian city's hosting of the 2018 Invictus Games.
Prime Minister Lee Hsien Loong says that Singapore has to work hard to tackle the situation of rising unemployment.
The SCDF preliminary investigations reveals that the explosion was likely caused by a road traffic accident.
The operations are part of efforts to ensure that massage establishments adhere to the rules and conditions of their licences.
The police say if convicted, he might face a jail sentence of up to 10 years along with a fine.