They're also an elite team of investigators solving some of the nation's biggest crimes.

Sometimes, using nothing more than a blot of ink.

Here we are: the lobby of the Secret Service.

These were the only authorized shots we could get.

Upstairs, in the lab, we got to see all the high-tech machines analysts use in forensic investigations.

They have names with things like 8,000 after them so you know they're complicated.

Did you film a printer?

I did.

The lab includes people like Trista, who specializes in handwriting analysis to investigate threat letters or ransom notes.

Jeffrey investigates fraudulent items like IDs, traveler's checks, credit cards.

And Irina, she works in the International Ink Library.

My name is Irina Geiman.

I am a document analyst with the United States Secret Service.

The Secret Service has the largest ink library in the world.

There are over 12,000 inks that are currently in the collection.

This includes pens, bottled ink, and printer cartridges.

Basically, this team of scientists is using ink to help solve crimes.

They're ink-vestigators.

Unh-uh, no, don't do that.

OK, so here's an example.

Someone writes a threatening letter to the President.

Irina will sample that ink and then compare it to her collection.

Exactly, she can figure out what kind of ink was used, and, hopefully, it helps solve the case.

Here's another ink-xample.

Nope, gimme that script.

The most counterfeited bank note within the United States is $20, and it's printed with inkjet, which means somebody takes their very simple at-home printer and decides to print money.

Irina can compare the counterfeit currency to any printers found at the scene of the crime and help make a match.

OK, time for a little science.

Here's why you need 12,000 samples of, let's be honest, mostly black ink.

A lot of the black inks are not just black.

They're actually a collection of different color components.

There could be blues then reds and yellows, and maybe a little bit of green.

Irina can, for lack of a better term, sequence black ink like you would DNA, and find the exact breakdown of color.

That's how she can make a match.

So what appears black at a first glance is actually extremely different on the inside, and it's really fun, as a chemist, to be able to take the ink apart and see how it's made.

I'm a nerd at heart.

I love the chemistry of it.

I love the mystery of solving a case.

I just really love what I do.

So it may not look exactly like it's on TV, but it's really fun to be in a lab and to be able to do the analysis and to be able to help and assist all the law enforcement agencies that I work with daily.

So, Irina, can you give us any more examples?

It's on a need to know basis, and you do not need to know.

Well, it looks like this case is all dried up.