As he had a duty to name names when he told the US Senate that he had witnessed war crimes in Vietnam.
What war crimes? He just talked about actions that he characterized as war crimes: free fire zones and the like. The only deaths he saw were accidental, resulting from policies he characterized as criminal, but which others did not.
The atrocities he did cite, where everyone would agree they were atrocities, were sourced to named individual witnesses in the Winter Soldier Investigation.