The body has been taken for post-mortem.
An investigation is underway in the case.
Singh, who was a junior level national champion boxer, had gone to the gym on Wednesday and since then his mobile phone was switched off.
The Gym's owner Pritam Tokas had found Singh shot dead in his flat after he went to see him.
"The miscreants had closed the door of the flat after killing Jitendra and also took his mobile along with them. Jitendra's mobile number has been put on surveillance and the CCTV footage in the apartment is also being scrutinized," said Greater Noida Superintendent of Police (SP) Suniti Singh.
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