i'm leland vittert. >> and i'm heather childers. we're in for uma peng ram u. "america's news headquarters" starts right now. >> we begin with the investigation into the downing of malaysian airlines flight 17, where international monitors have been trying to get better access to the crash site to see if the area has yet been compromised. >> jennifer griffin is monitoring the geopolitical fallout as ukraine accuses russia of helping separatist rebels disturb the evidence at the site. jennifer, what can you tell us? >> heather, senior western intelligence officials tell me they believe this video shows the actual sa-11 missile launcher used to bring down the malaysian plane. it is missing two of its four missiles and shows the missile launcher heading toward the russian border at dawn yesterday. u.s. officials now believe they have pinpointed the launch site for the missile that brought down the plane, inside ukraine.