Boulder, Colorado - The family of a man suspected of attacking a Jewish protest march with Molotov cocktails was being held by immigration officials Tuesday, the government said.

Kristi Noem, Homeland Security Secretary, said the wife and children of Mohamed Sabry Soliman had been detained.

"We are investigating to what extent his family knew about this heinous attack, if they had knowledge of it, or if they provided support to it," she said.

Criminal investigations are typically carried out by the FBI and local law enforcement, not by the Department of Homeland Security.

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Soliman's immigration status has been at the center of President Donald Trump's administration's response to the attack in the city of Boulder on Sunday, in which 12 people were injured.

Officials were quick to say he was in the US "illegally," having overstayed a tourist visa, but they also acknowledged he had applied for asylum and had been granted a work permit.

Soliman is expected to appear in court in Colorado on Thursday. He is expected to formally face federal hate crime charges, as well as state charges of attempted murder.

He is suspected of throwing flammable liquid at a group of older people marching to raise awareness of the Israeli hostages still being held by Hamas after the October 7, 2023 attacks.