The Hawaii Emergency Management Agency employee who sent a false alert about an incoming ballistic missile earlier this month has refused to cooperate with a Federal Communications Commission investigation, an FCC official said Thursday.

Lisa Fowlkes, chief of the FCC’s public safety and homeland security bureau, said she was “disappointed” during a hearing with the Senate Committee on Commerce, Science and Transportation.

“We are quite pleased with the level of cooperation we have received from the leadership of the Hawaii Emergency Management Agency thus far. We are disappointed, however, that one key employee, the person who transmitted the false alert, is refusing to cooperate with our investigation,” Fowlkes said on Thursday. “We hope that person will reconsider.”

A Jan. 13 emergency alert that went to millions of mobile phones sent waves of panic across the state. The message said, “BALLISTIC MISSILE THREAT INBOUND TO HAWAII. SEEK IMMEDIATE SHELTER. THIS IS NOT A DRILL.”

It took 38 minutes for authorities to correct the error and send a follow up message that the alert was a mistake.

The Hawaii Emergency Management Agency said Thursday it hoped its employee—who has already been reassigned—would decide to cooperate with the investigation.

“We share FCC Public Safety Bureau Chief Lisa Fowlkes’s disappointment. The Hawaii Emergency Management Agency has encouraged its employees to cooperate in all ongoing investigations, and while each individual makes a personal choice, we hope anyone who is not cooperating will reconsider and help to bring these matters to a satisfactory conclusion,” Richard Rapoza, the agency’s public information officer, said in a statement.

Despite the employee’s lack of cooperation, Fowlkes said the FCC’s investigation has made progress. She told to the Senate committee that officials in Hawaii have begun to change their procedures to ensure a similar mistake does not happen again.

“The Hawaii Emergency Management Agency tells us that is working with its vendor to integrate additional technical safeguards into its alert origination software, and has changed its protocols to require two individuals to sign off on the transmission of tests and live alerts,” she told the committee.

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Write to Abigail Abrams at abigail.abrams@time.com.