The state of Michigan’s inquiry into the Flint water crisis will consider any potential criminal conduct, including involuntary manslaughter, investigators said Tuesday.

Michigan attorney general Bill Schuette and a team of investigators appointed last month to examine Flint’s water debacle said they’ve “hit the ground running” in the investigation.

“As I’ve said for some time, to try to capture in words the tragedy of what occurred in Flint, it’s almost beyond description,” Schuette said during a roundtable with reporters.

The investigators declined to put a timeline on when the inquiry will be completed, but said the scope of potential criminal charges that may be considered include misconduct in office and involuntary manslaughter.

“If you have a duty and you breach that duty, [and] because of the gross negligence of that breach someone died, and you can show the proximate cause of that death reached to the breach, then you can have involuntary manslaughter,” said Todd Flood, a former county prosecutor. “It’s not far-fetched – it happens. We’ve had that before.”

Flint’s water supply was contaminated by lead, after the source of the city’s drinking water was switched from Lake Huron to the Flint river in April 2014. Water from the Flint river had for months corroded lead from the inside of water pipes before flowing into thousands of households across the city.

In the intervening 18-month period before the state conceded Flint’s drinking water was contaminated, state officials documented a spike of legionnaires’ disease in the area surrounding Flint, including nine deaths, but officials haven’t concluded the water source was the cause of the increase.

Asked whether Flood was referring to the deaths from legionnaires’ when he suggested an involuntary manslaughter charge, a spokeswoman said the charge was only hypothetical.

Schuette announced last month that Flood would serve as special counsel in the state’s investigation, and former Michigan FBI chief Andrew Arena will also investigate the crisis. Nine full-time investigators were handpicked by the group to examine what happened in Flint, which has rankled residents for nearly two years and has become an issue on the presidential campaign trail. A Democratic presidential debate is scheduled in the city on 6 March.

Deputy chief investigator Ellis Stafford, a Flint native, said he has a personal stake in the crisis.

“I gave a lot of people my word,” he said, adding: “They were in my wedding, they’re the godparents of my children. So I’m still going to have to see them. The only thing I’d ask is they give me a chance.”

The US Department of Justice, FBI and Environmental Protection Agency are each conducting separate investigations. Michigan governor Rick Snyder, who has been roundly criticized for his administration’s delayed response in addressing the crisis, appointed a task force in December to review the situation. An initial report by the taskforce chiefly blamed the Michigan department of environmental quality, which didn’t require Flint to use corrosion control to treat the local river water.

Several federal and state lawsuits have also been filed. Last month, as part of the suits, several state agencies were served a subpoena for all documents related to Flint’s drinking water dating back to 2011, including Snyder and his executive staff’s emails. The documents are expected to be produced by 1 March, and the state has yet to the challenge the subpoena.

Investigators declined to discuss which officials, if any, have been investigated so far or which documents have been reviewed. Schuette, whose office is both investigating the crisis and representing Snyder in the civil cases, refused on Tuesday to discuss the subpoena and its potential impact to the state’s investigation, citing an “ironclad” wall between the investigation and civil lawsuits he says his office has established.

“That is a different side of the conflict,” he said, adding that the civil cases are being handled by the state’s chief deputy attorney general.

Meanwhile, on Tuesday, Flint mayor Karen Weaver announced a $55m plan to replace the city’s network of lead service lines. The mayor said her proposal will require funding from the Michigan legislature or the US Congress.

“We’re going to get rid of these lead pipes one house at a time, one street at a time, one neighborhood at a time, until they’re all gone,” Weaver said in a statement Tuesday. “We have to start restoring people’s confidence and trust in our city’s water supply. We cannot afford to wait any longer.”

Officials from the city of Lansing, which has been involved in a years-long project to remove its lead pipes and is currently assisting Weaver, said the project could be completed in one year under optimal conditions.

“I invite Governor Snyder and his team to pledge their full cooperation to help us get this done,” Weaver said. “And I call on the legislature and Congress to appropriate the necessary funds so we can get started as soon as possible. The people of Flint have already paid with their lives, health and quality of life.”