After Marquis Wauter pinned the blame on the Demon Worshippers, King Lutheran Geyser could not help but inwardly.
Yes, the Demon Worshippers were the most likely suspects, but they aren't the only possible suspects.
For instance, King Lutheran Geyser was aware that a supremacist faction existed within the kingdom. Members of this faction are all unhappy with the situation on the western side of the Human Domain.
They believe that the Geyser Kingdom should rule over the entire Human Domain instead of being isolated to the eastern side.
Nevertheless, even if this supremacist faction had nothing to do with the envoys' deaths, they would still support the Demon Worshipper's war instigation between the two countries.
Thus, as Marquis Wauter mentioned, it was most likely the Demon Worshipper's work.