About 40-year-old grenades were found at Ilanthila in Belthangady taluk.
"We are investigating where they came from," Dakshina Kannada SP Rishikesh Sonawane said.
It was Jayakumar Poojary who had come across the grenades near a fence, while he was walking towards his house on Sunday evening.
Being an ex-serviceman, he kept them near his yard before informing the police fearing an explosion may hurt wild animals or the general public.
In his complaint, Poojary alleged that miscreants placed the grenades "for causing harm".
During the investigation, the police realised that the grenades were 40-year-old. The investigation is in progress, said the SP.
The Uppinangady Police have registered a case.
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