entering with the kosovo peace force back then, we discovered the horrors the former yugoslavia serbian troops committed on kosovo's muslim majority. >> reporter: u.s. forces rolling into kosovo get their first good look at just why they are here. dismay fills these young faces at the site of so many burned houses, at the stark evidence of ethnic cleansing. >> it is messed up. i'd hate to see this happen at home, and i hate to see it happen anywhere. >> reporter: it gets worse. this is the first mass burial site discovered by k4. u.s. troops are guarding it until war crimes investigators can exhume these 35 mounds of earth. there are reports of many more in kosovo. >> marines and infantry soldiers