WASHINGTON (AP) — The top Republican on the Senate Judiciary Committee says the events in Boston make clear the importance of understanding gaps and loopholes in the U.S. immigration system.

The attacks were allegedly carried out by two brothers from a Russian region near Chechnya.

Iowa Sen. Chuck Grassley says the attacks raise questions like how to beef up security checks on people who wish to enter the U.S.

Grassley spoke Friday at the first hearing on new bipartisan legislation to remake U.S. immigration laws.

The hearing was overshadowed by the drama in Boston, where police were hunting one of the brothers and the other was killed. Homeland Security Secretary Janet Napolitano had been scheduled to testify, but her appearance was canceled.