Analysis of the travel details of the accused -- who had gained access to the paid area of Rajendra Place station on Delhi Metro's blue line using smart cards -- showed that they often used to board and de-board the Metro at Kaushambi station on the same line, an official said.
Several teams have been set up to crack the case and CCTV footage is being studied with authorities trying to ascertain the identities of the accused, whose faces are slightly visible in one clip although both had come wearing masks, he said.
"A special team has been placed there. The team has also zeroed in on two youths whose faces match with that of the duo in the video clip," the official said.
The other stations frequented by the accused include Anand Vihar and Vaishali, respectively, the stops preceding and succeeding Kaushambi.
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He further said that the possible role of an insider is also being probed in the case.
Investigators are probing whether the duo had done a recce of the Rajendra Place station before executing the robbery early yesterday morning.
The possibility of them having done a recce emerged because the accused targeted the station control room directly, the official said.
Sleuths are also trying to determine whether the three- inch-knife recovered from the spot had been carried in by the accused or was already present inside the Metro station premises with CISF rejecting speculation in this regard saying the accused were frisked clean.
Earlier today, CISF issued a set of fresh instructions disallowing covering of the face by travellers using any kind of cloth or cover like surgical masks, mufflers, 'dupatta' or anti-pollution caps.
The two men, also captured on the CCTV, were wearing masks during their entry and exit from the station.