So, what you really have is a conflict between literary devices.

If you cut to 3rd person scenes, you create dramatic irony, as Robert Waltz points out.

But if you keep the whole story in 1st person, from the perspective of one main character, and that person is in the dark about a lot of things, then your reader will be in the dark, too. That creates suspense, which is arguably just as awesome of a literary device.

You could also change characters in 1st person. I like to reference "The Help" as a successful example of this, and the Divergent trilogy (specifically Book 3) as an example in which the voices are too similar to tell them apart.

Cheers,
Michelle