ALOHA, Ore. (AP) _ After the FBI agents left, Mona Mayfield wept at her kitchen table, then pulled herself together to survey the ransacked rooms. Closets had been emptied and drawers upturned.

``They took my children's Spanish homework,'' she said, a week after authorities arrested her husband, Brandon Mayfield, in connection with Spain's worst terrorist attack.

Mona Mayfield and other family members have been waiting to learn the fate of Brandon Mayfield, a Portland attorney and convert to Islam taken into custody at his suburban law office on May 6.

Although Mona Mayfield said her husband has not been out of the country since the 1990s, officials said his fingerprint were found on a plastic bag in a van near the Alcala de Henares train station outside Madrid.

The bag contained detonators that officials said were the same kind as those used to blow up four commuter trains in the Spanish capital on March 11, killing 191 people and injuring 2,000 others.

Eighteen people have been charged _ six with mass murder and the rest with belonging to a terrorist organization. Mayfield is the only American with links to the bombings, although he has not been charged with a crime.

Mayfield's family insists he is innocent. To them, the missing Spanish homework shows that federal agents are desperate to find evidence. ``They can turn anyone into a terrorist,'' Mona Mayfield said.

A former Army officer, Brandon Mayfield has not been outside the United States since serving at Air Force Base in Germany in the 1990s, she said.

According to senior law enforcement officials who spoke on condition of anonymity, the FBI is convinced the fingerprint in Madrid is Mayfield's.

Spanish officials and U.S. counterterrorism experts have raised doubts.

Three days after Mayfield's arrest, forensic experts in Spain told the newspaper El Pais that they found only eight points of similarity between the print on the plastic bag and Mayfield's _ far less than the 15 required for an exact match.

Senior U.S. law enforcement officials said Mayfield had been under surveillance for several weeks before his arrest. When it became clear that news about him might leak, the Justice Department placed him in custody, officials said.

It was a move that raised red flags for counterterrorism expert Michael Greenberger, a former U.S. Department of Justice official.

``The fact that they are using the material witness statute shows they don't have probable cause to arrest him,'' said Greenberger, who now heads the University of Maryland's Center for Health and Homeland Security. ``They're scrambling to find a way to detain him.''

Under the material witness statute, prosecutors can seek an arrest warrant and hold an individual without filing charges if the witness' testimony is considered crucial and there is a reasonable risk of the witness fleeing.

In the Bush administration's war on terror, the statute has been used to detain possible terror suspects without filing charges.

Nearby Portland has its own example _ one that proved doubters of an earlier terrorism investigation here wrong.

Mike Hawash, a former Intel software engineer, was arrested and held for five weeks without being charged. His case led to a public outcry and a ``Free Mike Hawash'' campaign.

However, six months later, Hawash pleaded guilty to conspiracy to wage war against the United States, as did five others accused of planning to help the Taliban fight American forces.

Mayfield has ties to Jeffrey Battle, one of the six, whom he represented in a custody hearing involving his child. Family members say a local mosque approached Mayfield, asking him to take the case.

Quanell X, head of the New Black Muslim Movement in Houston and a Battle family friend, said Mayfield went out of his way to help Battle, flying to Texas, on his own money to represent the terrorism suspect in the child custody dispute.

Mayfield had converted to Islam after marrying Mona, a Muslim who immigrated to rural Washington as a child.

Mayfield's mother, AvNell, and his younger brother have taken a leave of absence from their jobs in Kansas to be with Mona. The Mayfields' three children, ages 10, 12 and 15, have been provided security at their local schools.

``Either charge him, so he can defend himself, or set him free,'' said Kent Mayfield, 35, the attorney's brother. ``In the meantime, peoples' lives are being destroyed.''