BTP Message Verifier (BMV) is a smart contract that extracts a relay message, which is composed of a BTP message with proof of existence, to the BTP message before verifying. For easy verification, it may update trust information for the following events. Most of the implementations may track the hashes of block headers. If the blockchain system provides proof of absence of the BTP messages, then it's enough for the verifier to sustain the last state only. It updates the hash only if it sees proof of absence of further BTP messages in the block. Most blockchain systems don't provide proof of absence for their data. Therefore, it is mandatory to provide methods to verify historical hashes. Merkle Accumulator can be used for verifying old hashes. BMV sustains roots of Merkle Tree Accumulator, and relay will sustain all elements of Merkle Tree Accumulator. The relay may make the proof of any one of old hashes. So, even if byzantine relay updated the trust information with the proof of a new block, a normal relay can send BTP Messages in the past block with the proof.