NEW HAVEN, Conn. (WTNH) — New Haven lost $6 million in a “significant cyberattack” that targeted the city’s school district, officials announced on Thursday.

Leaders said the city has been a victim of several cyberattacks since May. Hackers were able to get access to the emails for the chief operation officer of New Haven Public Schools.

Mayor Justin Elicker said that the hackers watched the email exchanges between the district’s COO, the city’s budget office and vendors. The criminals then impersonated the COO and made six successful electronic money transfers.

“The individual or the individuals that did this are criminal,” Elicker said. “They’re unbelievably unethical to not only steal money from the public, but steal money from New Haven Public School children. It is just shocking to me how much greed there is in this world today, and that someone would so deliberately do such a thing is just tragic.”

Four of those transactions were for a collective $5.9 million that was meant for the First Student Bus Company. The other two were for more than $76,000 to the Shipman and Goodwin Law firm.

“New Haven Public Schools alerted us that the district was the victim of a cybercrime involving funds intended for First Student,” a statement from the company reads. “We are a longtime partner of the district and are ready to further assist in the ongoing investigation of this crime against the New Haven Public Schools and taxpayers.”

Elicker said the city learned about the transactions in late June. The FBI and New Haven Police Department are continuing to investigate the crime.

So far, investigators have been able to recover $3.6 million of the funds. Officials have frozen additional transactions. The city has also stopped electronic transfers, with an exception for payroll.

Leaders have cleared city staff of any criminal wrongdoing. Meanwhile, an employee in the budget office is on paid administrative leave.