I did as you suggested. Here is an excerpt from the CATO Institute's site:
"An unambiguous federal statute and the U.S. Constitution both prohibit the
executive branch from doing to Padilla what it is now doing. More than three
decades ago, Congress passed Title 18, section 4001(a) of the U.S. Code. It
states, "No citizen shall be imprisoned or otherwise detained by the United
States except pursuant to an Act of Congress." Today, we have not had from
Congress any statute that authorizes Padilla's detention.
Yes, Congress enacted the PATRIOT Act, which says that non-citizens suspected of
terrorism can be detained, but only for seven days. After that, they have to be
released or charged, unless the attorney general certifies every six months that
they present a security risk. Two months earlier, Congress had passed a
resolution empowering the president to use all necessary force against the 9/11
terrorists. But that resolution surely did not give the administration
unfettered discretion to detain citizens without charge. If it had, then the
ensuing PATRIOT Act would have afforded more protection to aliens than to
citizens. In the wake of the 9/11 attacks, that proposition is incredible."
This seems to make it pretty clear that the Patriot Act was not the basis for
the detention of Padilla. It also provides an indication of why there are so
many hits when googling "jose padilla patriot act" (without the quotes, of
course).