What is one of the key elements to link a current condition to military service?

The existence of medical records is a key element in linking a current condition to military service because these records provide objective, documented evidence of a veteran's health status and any medical issues that arose during or after their time in service. Medical records can include details about injuries, treatment received, diagnoses, and any ongoing health issues that can substantiate claims for service connection.

Having well-documented medical records can significantly enhance the credibility of a veteran's claim. They not only serve to show that a condition exists, but they can also assist in establishing a timeline of events, demonstrating that a medical condition began during service or was exacerbated by military duties.

Other options like a direct eyewitness account or a veteran's self-reported symptoms may provide context or support for a claim, but they lack the formal documentation that medical records provide. A comprehensive service history can be useful in many ways, but it doesn’t specifically demonstrate current medical conditions or their connection to service as effectively as medical records do.