"As per preliminary findings of the postmortem report, some poisonous content was found in Gupta's body," said Ayodhya Nagar police station in-charge Baljeet Singh.
However, the exact cause of Mr Gupta's death could be ascertained only after a comprehensive report of autopsy is available, he said.
"We are awaiting the postmortem report," he said, adding that further investigation is underway.
The officer said they would take a call on registering a case in the matter once the PM report is available. Mr Gupta was posted at Jodhpur Airbase and was on leave.
Mr Gupta's father Dr Rajesh Gupta said his son stepped out of their house in Old Minal Residency Colony on June 4 morning.
"He returned home late night and went to sleep after dinner. On Tuesday morning, he complained of breathing difficulty and stiffness in his chest," Rajesh Gupta said.
He said Himanshu Gupta was rushed to a nearby hospital before he was shifted to state-run JP Hospital, where he died on Tuesday.
"We don't know what happened to him," he said.