Section 61(1)(a) in The Goa Panchayat and Zilla Panchayat (Election Procedure) Rules, 1996
(a)any ballot box used at a polling station is unlawfully taken out of the custody of the Presiding Officer or the Returning Officer, or is accidentally or intentionally destroyed or lost or damaged or tampered with to such an extent, that the result of the poll at that polling station cannot be ascertained, or