A Detroit congressman on Tuesday visited the jailed co-founder of an Islamic charity that was closed down as part of the terrorism investigation and expressed doubts concerning his continued detention.

"There does not on the surface seem to be any reason why he should not be released on his own recognizance," Democratic U.S. Rep. John Conyers told a rally outside Chicago's Metropolitan Correctional Center.

Rabih Haddad, 41, of Ann Arbor, Mich., has been held for overstaying his visa since his arrest Dec. 14, the same day agents raided the Global Relief Foundation, an Islamic charitable organization.

Haddad was a co-founder of the group, based in the Chicago suburb of Bridgeview. The government says the group is suspected of funding terrorist operations overseas. Global Relief denies that and says that it sends money to Islamic countries for humanitarian purposes only.

While Haddad is being held only on an immigration charge, it would appear that the government's interest in him runs deeper. He appeared before a federal grand jury on Feb. 14 but exercised his Fifth Amendment rights against self-incrimination, Global Relief attorney Ashraf Nubani said.

Nubani said he was the one who advised Haddad to invoke the Fifth Amendment because Haddad had been held in solitary confinement in a cell without a window and had not had adequate access to a lawyer.

He said he did not want Haddad speaking to a grand jury under those circumstances unless he had immunity from prosecution.

Global Relief had issued a statement on Feb. 14 saying that Nubani had appeared before the grand jury and that the group was cooperating in the federal investigation. The statement said Nubani had advised Haddad not to answer "substantive questions" unless he had assurances that his answers would not be used against him in a criminal or immigration case.

Conyers said he met with Haddad for an hour and found him to be in good spirits. He said Haddad had only recently had his first so-called "contact visit" with his wife. Previous visits were through glass partitions using a telephone, Conyers said.

Conyers said that Haddad "is not getting due process. He has at times been denied access to his lawyer." He stopped short of calling for his release but said that keeping Haddad locked up "raises questions about how the Department of Justice is proceeding."

Haddad's attorneys have not contested the right of the government to hold him for his expired U.S. visa.

Asked how long the government could hold his client under federal immigration law, Nubani said: "As the setup is now, indefinitely, unfortunately."