FLINT, Mich. » The FBI is working with a multi-agency team investigating the lead contamination of Flint’s drinking water, alongside Environmental Protection Agency investigators who can tackle criminal violations of federal environmental law, officials said today.

Several local, state and federal officials have resigned since doctors revealed last year that using the Flint River for the city’s drinking water supply caused elevated levels of lead in some children’s blood. Lead contamination has been linked to learning disabilities and other problems. Michigan’s governor has apologized repeatedly for the state’s role.

FBI spokeswoman Jill Washburn told the AP in an email that the agency’s role is “investigating the matter to determine if there have been any federal violations.” She declined to say when the FBI got involved.

Officials haven’t said whether criminal or civil charges might follow the investigation.

In addition to the FBI and the EPA, the team includes the U.S. Postal Inspection Service, Gina Balaya, a U.S. attorney’s spokeswoman in Detroit, told The Associated Press in an email. The Detroit Free Press first reported the FBI’s involvement today.

In November, the EPA announced it was auditing how Michigan enforces drinking water rules and said it would identify how to strengthen state oversight. The U.S. attorney’s office in Detroit said in January that it was investigating the water crisis with the EPA.

Flint switched its water source from Detroit’s water system to the Flint River in 2014 to save money while under state financial management. The river water was not treated properly and lead from pipes leached into Flint homes. The city returned to Detroit’s system in October while it awaits the completion of a separate pipeline to Lake Huron this summer.

The U.S. House Oversight and Government Reform Committee is expected to hold a hearing Wednesday on Flint’s water crisis. Detroit schools emergency manager Darnell Earley, who was state-appointed emergency manager for Flint when its water source was switched, had been asked to testify but declined the invitation, Detroit Public Schools spokeswoman Michelle Zdrodowski said in an email.

The federal investigation is one of several taking place into Flint’s water supply. Last month, Michigan Attorney General Bill Schuette announced the appointment of a special counsel to help his office investigate whether laws were broken.

An independent panel appointed by Gov. Rick Snyder has determined that the Michigan Department of Environmental Quality was primarily responsible for the water contamination. The Michigan Civil Rights Commission also plans to hold hearings to explore whether the civil rights of Flint residents were violated.