oil field. nic robertson joins us from riyadh with all the new details. what have you learned? >> reporter: what we're hearing from a source familiar with the investigation gives us some understanding of why secretary of state mike pompeo may have said very quickly that iran was responsible. and perhaps gives more understanding as well why the saudis officially said yesterday these weapon systems were made by iran. now what we learned from this source is that some of the missiles that were fired at this plant fell short. they fell in the desert to the north of this petroleum facility. that gives the indication the weapons were coming from the north, not from the south as the houthis said. because they fell into the desert, they didn't explode properly which is giving the u.s. and saudi investigators good, quality evidence. unexploded missile parts to