The cartridges were recovered from outside Hotel Ashok situated in the high-security Chanakyapuri locality on January 28.
Investigations began after hotel authorities lodged a complaint with police claiming that there was some firing incident outside its gate besides handing over the empty cartridges.
A senior police official said they have received the complaint and investigations were on.
When contacted, Additional Commissioner (New Delhi) Shankar Dass said that the matter was reported by the hotel authorities well after 12 hours of the incident.
"We don't know why the hotel authorities took 12 hours to inform us. They should have called 100 soon after the incident. We are investigating the matter," Dass said.
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