The head of the Senate Judiciary Committee is demanding that the Obama administration provide details about the gunman believed to have killed 49 people in an Orlando nightclub this weekend.

Sen. Chuck Grassley (R-Iowa) told the administration that he needs a “more thorough understanding” of Omar Mateen’s alleged connections to the Islamic State in Iraq and Syria (ISIS) “and what motivated this act of terror.”

Grassley asked the Departments of State and Homeland Security for files that have been requested as part of the ongoing terrorist investigation into Mateen as well as the criminal and travel records of him and his family members.

Among other points, Grassley asked whether anyone in Mateen’s family had ever applied for refugee status in the U.S., which terrorist watch lists he had appeared on and whether his parents had ever returned to their native country of Afghanistan.

Grassley also asked whether Mateen had ever worked for the Homeland Security or State departments.

A copy of the letter was also sent to the FBI.

The inquiry from Grassley is among the first formal efforts by Capitol Hill to get up to speed on the weekend killing at a gay nightclub, the deadliest mass shooting in U.S. history.

Fallout from the shooting has spiraled in multiple directions.

Donald Trump, the presumptive Republican presidential nominee, has focused in on questions of immigration, using the shooting to amplify his call to ban Muslims from entering the U.S. On Monday, Trump appeared to evolve on the policy, saying the U.S. should prohibit migration from countries with “a proven history of terrorism against the United States, Europe or our allies.”

Mateen was born in the U.S. to immigrants from Afghanistan. He told a 911 dispatcher that he had pledged allegiance to the leader of ISIS shortly before his death in a shootout with law enforcement, but he also appeared to express support for other extremist groups, complicating the FBI’s understanding of his motivations.

The 29-year-old had appeared on the FBI’s radar before, raising scrutiny on the bureau.

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