The SQL Server transaction log records changes made to the database, including data modifications (INSERT/UPDATE/DELETE) and many schema-related operations, supporting reconstruction of what changed and when. For unauthorized modifications, the transaction log provides the strongest evidence trail because it is tied to the database engine’s durability mechanism and captures the sequence of committed actions. In SOC investigations, transaction log analysis helps determine whether data was altered, which tables were impacted, and the time window of changes. Security logs or SQL Server security-related events help with authentication/authorization and may show login activity, but they do not reliably enumerate every data modification. Maintenance logs relate to scheduled maintenance tasks (backups, index rebuilds) and are not designed to capture unauthorized content changes. Audit logs can be extremely useful if SQL Server auditing is configured to capture specific actions and statements, but the question asks which log helps identify whether modifications occurred; the transaction log is the baseline record of actual database changes. In practice, SOC teams correlate transaction log evidence with authentication logs, application logs, and potentially SQL auditing to attribute actions to accounts and sessions, then scope and remediate.