That a head of state has been killed in battle by another person is a historical fact established by direct observation and general knowledge, requiring no formal citation.
The claim states that a head of state has been killed in battle by another person (such as Richard III at Bosworth Field or King Harold at Hastings). This is a matter of common historical observation and general knowledge rather than an empirical proposition requiring scientific literature to verify. Therefore, following the instructions for STEP 0, the verdict is COMMON_KNOWLEDGE and no citation is needed.