Tairod Nathan Webster Pugh, accused of making the foiled attempt in January, was indicted by a grand jury this week on charges of trying to give material support to the terror group and obstruction of justice, the U.S. Justice Department said.
Among the evidence, prosecutors allege: Investigators discovered on his laptop computer recent Internet searches for information on "borders controlled by Islamic state," and a chart of crossing points between Turkey and Syria, where ISIS controls some territory.
Pugh, 47, was arrested upon his return to the United States in January and will be arraigned Wednesday in a federal court in New York, the Justice Department said.
"Pugh, an American citizen and former member of our military, allegedly abandoned his allegiance to the United States and sought to provide material support to ISIL," Assistant U.S. Attorney General John Carlin said, using an alternate acronym for the Islamist terror group that controls territory in parts of Iraq and Syria.
Pugh will plead not guilty, his attorney, Michael Schneider, said.
The defendant, a former avionics instrument system specialist in the Air Force from 1986 to 1990, flew from Egypt to Turkey on January 10, weeks after being fired from a Middle East-based job as an airplane mechanic, U.S. authorities allege.
But Turkey denied him entry. In the indictment, U.S. authorities said Turkey was likely suspicious Pugh was headed for Syria.
Instead Turkish officials sent him on a return flight to Egypt, where he was detained. In Egypt, he was carrying multiple electronic devices, "including four USB thumb drives that had been stripped of their plastic casings and an iPod that had been wiped clean of data," the Justice Department said in a statement. Pugh had purposefully tampered with the devices to prevent others from getting access to his electronic media, the indictment said.
Pugh was deported to the United States, where agents with the FBI's Joint Terrorism Task Force obtained a warrant for his devices, including the laptop, the department said.
Investigators found a letter from January addressed to a Misha, whom they believe is his wife, authorities said. In it the writer says: "I am a (Mujahedeen). I am a sword against the oppressor and a shield for the oppressed. I will use the talents and skills given to me by Allah to establish and defend the Islamic States."
Besides the Internet searches and Turkey/Syria border chart, agents found "Internet searches for 'Flames of War,' an ISIL propaganda video, as well as downloaded videos, including one showing ISIL members executing prisoners," the Justice Department said.
They also found what the government said was 180 jihadist propaganda videos, one of which showed ISIS members executing prisoners.
Pugh was arrested in Asbury Park, New Jersey, on January 16.
While in the service, he was trained in installing and maintaining aircraft engine, navigation and weapons systems, the Justice Department said. The indictment says that he took a job as a mechanic with American Airlines in or about 2001.
From October 2009 to March 2010, he worked in Iraq as an Army contractor for DynCorp.
If convicted, Pugh could be sentenced to up to 35 years in prison.