Intel on 'two-hour timer' uncovered in Russian jet crash investigation

Investigators analyzing the deadly crash of a Russian jet in Egypt uncovered intelligence about a “a two-hour timer,”  though it is not clear whether the reference came from intercepted communications between known terrorist operatives, or physical evidence, a source familiar with the investigation told Fox News.

A separate source, also not authorized to speak on the record, said that based on the facts so far, one of the working theories is that a bomb was planted at or near the fuel line or where it attaches to the engine, with the fuel burning off the explosive. This theory would explain the apparent lack of residue immediately found, the source says.

"If proven accurate, if ISIS did put a bomb on this aircraft which I believe to be true, it's a new chapter with respect to ISIS," Texas Republican Rep. Mike McCaul told Fox News. McCaul -- who receives regular briefings -- cannot discuss classified information, but said the Obama administration has consistently underestimated ISIS by emphasizing its focus on gaining territory, rather than expanding its reach to global plots.

"We always assumed Al Qaeda had this capability but now if ISIS has this capability, the threat to American airlines as well and our homeland, I think is very significant."