Earlier this month, Singh was arrested in J&K's Kulgam, while ferrying terrorists of the Hizbul Mujahideen (HM).
Along with Singh, four others accused in the case were sent to NIA custody.
Here are more details.
NIA had sought custody of Singh, 4 others, for interrogation
Singh was produced in a special court in Jammu on Thursday along with the two HM terrorists he was caught with and two of their associates, PTI reported.
One Syed Irfan was also produced before the court. Irfan is the brother of one of the accused HM terrorists.
The NIA had sought 15-day NIA custody of the five persons for interrogation, which was granted.
Singh was caught traveling with terrorists on January 11
On January 11, Singh was intercepted by cops in Kulgam with two HM terrorists and one overground HM worker.
An initial probe found that Singh had sheltered the terrorists at his home in Srinagar and suggested that he was planning to move them out of J&K to Delhi.
Investigators are probing to see if their movements were linked to the upcoming Republic Day celebrations.
NIA probing Singh's involvement with HM, LeT, etc.
Singh was arrested, and last weekend, the counter-terrorism agency NIA took over the probe.
The NIA has conducted searches at Singh's Srinagar residence, where the police had previously found arms.
The agency is also investigating the cop's involvement with Hizbul Mujahideen, Jaish-e-Mohammad, Lashkar-e-Taiba along with other terrorist groups.
On Wednesday, the NIA had questioned Singh for allegedly helping the terrorists travel out of J&K.
Singh infiltrated HM for R&AW: Report
Meanwhile, intelligence and police sources told News18 that Singh was part of an operation to infiltrate HM for the Research and Analysis Wing (R&AW). However, Singh reportedly didn't seek authorization from R&AW before accepting Rs. 1.2 lakh from the terrorists in exchange for transporting them.
2001 Parliament attack convict had alleged Singh framed him
Singh was appointed to J&K Police's Special Operations Group (SOG) in 1994 and rose through the ranks.
However, he faced allegations of extortion and links to drug cartels over time.
In a 2004 letter to his lawyer, the 2001 Parliament attack convict Afzal Guru accused Singh of framing him.
Guru had alleged that Singh made him take another Parliament attack accused to Delhi.