Intel employee, US citizen Mike Hawash detained without due process

In an open letter to senator Ron Wyden (D-OR), Intel SVP Steven McGeady writes:

On Thursday morning, March 20, a long-time employee of mine, Mike
(Maher) Hawash, was arrested outside Intel's Hillsboro offices and
taken into custody by the FBI and members of the Joint Terrorism Task
Force. We later learned he was being "detained" as a material witness.
Simultaneously, FBI agents in bulletproof vests and carrying M-16s woke
Mike's wife and three children in their Hillsboro home, searched it for
four hours, and presented Mrs. Hawash with a grand jury subpoena.

All of the court documents in this case are sealed. Mike was held
incommunicado from his wife and attorneys for several days. When they
did contact him, neither he, his attorneys, nor anyone else knows why
he is being detained.
Mike is a long-time U.S. citizen, originally of Palestinian birth and
previously of Jordanian nationality. He has been a U.S. citizen for
many years, having attended college in Texas. He worked for me at Intel
on and off for 10 years. (…)

The only thing anyone can think of is that, long before 9/11/01, Mike
and his wife donated to Global Relief, a once-respected international
aid organization that since October 2002 has fallen into disrepute. But
there is no way Mike could have known this at this time. My wife is a
recently-naturalized U.S. citizen, originally from Northern Ireland,
another victim of terrorism. If our donations to Northern Irish aid
were to be mis-directed, without our knowledge, would I have FBI agents
kicking down my door? Would my wife be put into federal prison?