Boston Marathon Attack Could Impede 'Gang of 8' Immigration Bill

The question of whether international terrorism was involved in the Boston Marathon bombing is an argument to pass the immigration reform bill unveiled this week by a bipartisan group of senators, Arizona Republican John McCain told CNBC on Thursday.

"We're going to require e-verify documentation that someone is here legally, but also more importantly, exit as well as entry checking on everybody who enters and leaves this country," McCain said in a "Squawk Box" interview.

(Read More: Coalition Behind U.S. Immigration Bill May Be Fragile)

The immigration bill, sponsored by four Republicans and four Democrats, was conceived as a pathway to legal status for millions of immigrants.

But it also creates an entirely new system designed to increase the flow of foreign workers for lower-skilled U.S. agriculture and construction jobs, as well as, higher-skilled labor for in-demand technology positions.

In an interview earlier this week with National Review Online, Rep. Steve King, R-Iowa, said lawmakers should proceed with caution on immigration legislation because it's not known yet who's responsible for the Boston attack.

Investigators have not determined whether the attack was foreign or domestic terrorism.

(Read More: Complete Coverage of the Boston Marathon Bombing)

Sen. Charles Schumer, D-N.Y., who along with McCain is part of the so-called Gang of 8, told CNBC on Thursday that their approach to overhauling the nation's immigration procedures considered the types of issues raised by the marathon bombing.

"We've thought about students who overstay their visas and just stay in the country for a long period of time," Schumer said. "We've thought about improving the biometrics so people can't forge their identities. And that's part of our bill."

Authorities in Boston said they had searched the home of a 20-year-old man who is in the U.S. on a valid student visa. He has not been named a suspect.

NBC News reported that officials in Boston are searching for two possible suspects seen on camera, including one man who appears to setting down a black bag and running away just before the bombs went off.

By CNBC's Matthew J. Belvedere; Follow him on Twitter @Matt_SquawkCNBC. Reuters also contributed to this report.