(CNN) — FBI agents raided a residence in Metro Detroit last Friday in connection to threats made to the judge, two defense attorneys and at least one potential witness in the ongoing federal trial of four men accused of plotting to kidnap Michigan Gov. Gretchen Whitmer.

District Judge Robert Jonker and the attorneys for defendants Adam Fox and Barry Croft received threats in connection to the trial, Detroit FBI Special Agent Mara Schneider confirmed to CNN.

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The nature of the threats has not been disclosed to the public. No arrests have been made in connection to the threats, according to Schneider.

It is unclear if the federal courthouse in Grand Rapids has increased security measures for the trial as a result of the threats on trial participants. Prosecutors rested their case Wednesday morning.

Fox, Croft, Daniel Harris and Brandon Caserta face federal charges for allegedly conspiring to kidnap the Democratic governor in 2020. All have pleaded not guilty.

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Fox, Croft and Harris face additional charges of conspiring to use weapons of mass destruction including explosive devices, according to court documents.

Paid confidential informant Stephen Robeson also received threats, according to the FBI.

Robeson, who has not yet testified in the case, informed the court that he’ll invoke his Fifth Amendment right not to incriminate himself if he’s called to testify in a defense case.

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