 -- New evidence in the investigation of the Russian airliner that crashed in Egypt indicates an inside man may have helped to plant an explosive device on board, aviation security officials told ABC News.

Investigators today will be scrutinizing surveillance tape and employee records at Egypt's Sharm el Sheikh airport, from which the Russian jet took off, looking for a ramp worker who authorities say may have been recruited by ISIS to plant a bomb on the plane.

"ISIS may have concluded that the best way to defeat airport defenses is not to go through them but to go around them with the help of somebody on the inside," Rep. Adam Schiff, D-Calif., who has received classified briefings on the investigation, said on ABC News' "This Week" Sunday.

American authorities told ABC News that electronic intercepts of ISIS, both before and after the crash, indicated that ISIS was in communication with someone at the airport.

The first hard evidence of a possible bomb was revealed this weekend by Egyptian officials who said the cockpit voice recorder, the CVR, captured a distinct but undetermined noise just before it stopped working.

"A noise was heard in the last second of the CVR recording," an Egyptian official said.

U.S. experts say it is possible to determine if that noise was a bomb, and if so, where it was placed.

"[The noise of a bomb] is very sudden, very sharp. It has a very distinctive profile to it," said accident investigator and veteran former NTSB official Tom Haueter. "So you can tell bombs. Actually, they stand out."

Though authorities have not officially declared a bomb is to blame for the deaths of over 200 people last Saturday, former Department of Homeland Security undersecretary John Cohen said security officials are likely already "very concerned about copycats -- other people replicating the techniques used in this incident to conduct another attack."

ABC News' Molly Hunter, Josh Margolin and Patrick Reevell and freelance journalist Maggie Ghobrial contributed to this report.