I believe the Marine.
Fine. But what if the formal Marine investigation shows that the accusations are true? What then? Will you believe the Marine over the report?
I'm trusting the Marine Corps to conduct a fair investigation. If their report shows the troops behaved correctly then that should be the end of it. But if the reports shows that they did murder those people then their actions are a slander on every Marine and at the very least they should spend the rest of their days at Leavenworth.