Officials at the office of Attorney General Patrick C. Lynch learned up close the “widespread nature of the problem” of illegal immigration yesterday when one of two custodians who clean the law office of the state’s top prosecutor emerged as a likely illegal immigrant, said a spokesman.

The 32-year-old woman from Guatemala failed to show up for work Wednesday evening, one day after immigration officials arrested 31 suspected illegal immigrants working in the state’s courthouses.

When investigators asked immigration officials to check the documents that the woman provided in April for employment, they learned that her Social Security card and “resident alien card” were “evidently fraudulent,” said spokesman Michael J. Healey.

Custodians who work in the attorney general’s office are routinely subjected to criminal background checks, Healey said. But those checks are only as good as the information the prospective employee offers.

“In light of the events of this week, we’ve now also begun a fingerprint check,” Healey said.

The other custodian in the office was fingerprinted yesterday when he arrived for work and passed a criminal background check, Healey said.

The workers are employees of Falcon Maintenance Co. LLC, said Healey.

The attorney general’s office is staffed around the clock by investigators of the Bureau of Criminal Identification. The custodians are usually out of the building by around 8 p.m., said Healey, adding they do not have access to any sensitive material.

Speaking of the female custodian, Healey said, “We hoped she would come back and do a fingerprint check but certainly her conduct in the last day or so would indicate someone who is afraid of something. So it does speak to the widespread nature of the problem and we now have a new [screening] policy … so we feel confident going forward.”

tmooney@projo.com