Iowa Code § 804.11: Arrest of material witness.

1. When a law enforcement officer has probable cause to believe that a person is a necessary and material witness to a felony and that such person might be unavailable for service of a subpoena, the officer may arrest such person as a material witness with or without an arrest warrant.

2. At the time of the arrest, the law enforcement officer shall inform the person of:

a. The officer’s identity as a law enforcement officer.

b. The reason for the arrest which is that the person is believed to be a material witness to an identified felony and that the person might be unavailable for service of a subpoena.