The alleged mastermind behind the marmoset theft from the Alipore zoo escaped from the custody of Bhubaneswar police early on Friday while being brought to Calcutta by train.

This is the second time in eight weeks that the marmoset gang has caught the cops napping. A handcuffed Rajesh Singh, escorted by a havildar and two constables, followed in the footsteps of co-accused Raj Saikia, who had walked off the Ahmedabad Express at Jharsuguda station in Orissa, only to be rearrested within hours.

A probe revealed that all four minders of Saikia — an inspector, a sub-inspector and two constables — had fallen asleep while escorting him to the city early on August 31.

Sources in Lalbazar suspect that a similar lapse on the part of the Bhubaneswar cops — havildar Mirza Aslam Beg and constables A. Marandi and R. Soren — allowed Singh to give them the slip on the Puri-Howrah Express. There was no trace of the mastermind till late on Friday.

Damayanti Sen, the deputy commissioner of the detective department, admitted that Singh’s escape was a setback for the marmoset theft probe, now in its final leg.

She said Lalbazar was yet to hear from Bhubaneswar police about the 35-year-old — taken to Orissa a month ago in connection with his alleged role in the theft of a pair of macaws from Nandankanan zoo — even almost a day after he went missing.

The city cops came to know about the incident from the Kharagpur GRP, which had registered an FIR by Beg.

According to the complaint, one end of Singh’s cuffs was locked to the chain of his berth. When the train was entering Kharagpur around 2.45am, the cops noticed that the cuffs were dangling — without Singh.

Arrested in Rajasthan’s Ajmer on September 6, he is an old hand not just at stealing rare animals from zoos but also at fooling the cops.

An officer of the detective department said Singh, whose ancestral house is in Punjab’s Karnal, started off as a drug peddler. “He fled from police custody while being taken to court nine years ago. Since then he had been to several places before settling down in Ajmer,” said an officer.

The theft of the eight marmosets, rare monkeys of Brazilian origin, came to light on August 9. Sleuths said Singh, who masterminded the theft, had received Rs 2 lakh from a 72-year-old Pune resident, Vivian Solesman.

Seven of the marmosets were recovered in Durg on August 28. One animal was reported to have died.