– The FBI is now investigating the contamination of Flint’s drinking water, a man-made public health catastrophe, which has left an unknown number of Flint children and other residents poisoned by lead and resulted in state and federal emergency declarations.

Gina Balaya, a spokeswoman for the U.S. attorney’s office in Detroit, said that federal prosecutors are “working with a multiagency investigation team on the Flint water contamination matter, including the FBI, the U.S. Postal Inspection Service, the Environmental Protection Agency’s Office of Inspector General, and EPA’s Criminal Investigation Division.”

The office of U.S. Attorney Barbara McQuade said Jan. 5 that it was assisting the U.S. EPA in a Flint drinking water investigation, but at that time, Balaya would not say whether the investigation was civil or criminal.

Balaya disclosed the involvement of the FBI and other agencies that investigate potential criminal wrongdoing when asked whether there were any concerns about the EPA leading the federal investigation, given the resignation of an EPA regional director over the crisis and public criticism of the EPA’s conduct.

The EPA’s Office of Inspector General is an independent office within EPA that performs audits, evaluations and investigations of EPA and its contractors to prevent and detect fraud, waste and abuse. The EPA’s Criminal Investigation Division investigates potential criminal violations of federal environmental law.

Jill Washburn, a spokeswoman for the FBI in Detroit, confirmed Tuesday that the FBI is involved in the investigation but would not say when that involvement began. “Our role is to determine whether or not there have been federal violations,” Washburn said.

The disclosure of the FBI’s involvement in the investigation comes as the U.S. House Oversight Committee prepares to hold its first hearing on the issue Wednesday, amid reports that former Flint emergency manager Darnell Earley will decline to testify.

Earley is now emergency manager of Detroit Public Schools, but Gov. Rick Snyder’s office announced Tuesday that Earley will step down effective Feb. 29.

The existence of criminal investigations raises the possibility that some witnesses could exercise their Fifth Amendment rights against self-incrimination and decline to testify before congressional hearings.

Flint’s drinking water became contaminated with lead in April 2014 after the city, while under the control of a state-appointed emergency manager, temporarily switched its source from Lake Huron water treated by the Detroit Water and Sewerage Department to water from the Flint River.

Department of Environmental Quality Director Dan Wyant resigned in December after acknowledging that the DEQ failed to require the addition of needed corrosion-control chemicals to the corrosive Flint River water. As a result, lead leached from pipes, joints and fixtures, contaminating the drinking water for an unknown number of Flint households. Lead causes permanent brain damage in children, as well as other health problems.

For months, state officials downplayed reports of lead in the water and a spike in the lead levels in the blood of Flint children before acknowledging a problem Oct. 1. Since then, Snyder has faced questions about when he first knew there was too much lead in Flint’s drinking water.

A task force named by Snyder also is investigating, as is Michigan Attorney General Bill Schuette, who appointed former Wayne County assistant prosecutor Todd Flood and former Detroit FBI director Andrew Arena to lead the investigation by his office.