The U.S. National Transportation Safety Board is looking at issues raised by more than one whistleblower as it investigates battery failures that have grounded the global fleet of 50 Boeing Co 787 Dreamliners for a week.

Michael Leon, one of the whistleblowers, said he spoke with an NTSB investigator this week and gave him extensive materials about his claim that he was fired around six years ago for raising safety concerns about Securaplane Technologies Inc., an Arizona company that makes chargers for the highly flammable lithium-ion batteries at the heart of the probe.

In an interview with Reuters on Wednesday and in earlier court papers, Leon said Securaplane was rushing to ship chargers that by his assessment did not conform to specifications and could have malfunctioned.

A federal administrative judge later dismissed Leon’s complaints after concluding he was fired for repeated misconduct, according to court documents. The Federal Aviation Administration (FAA) concluded that the pieces of equipment he complained about were never installed in the aircraft, as they were prototypes.

Leon appealed the federal court’s ruling in 2011, but no decision has been reached.

Now the NTSB is taking a closer look at some safety concerns people have previously raised as part of a widening investigation by U.S., Japanese and French authorities into two 787 battery failures this month. One involved a fire on a parked 787 at Boston airport, the other forced a second 787 to make an emergency landing in Japan.

Kelly Nantel, NTSB director of public affairs, confirmed the NTSB was pursuing information provided by “more than one” whistleblower, but declined comment on any specific cases.

“We have been notified about whistleblowers and are pursuing that information where warranted,” Nantel told Reuters, adding it was “not uncommon” for individuals to come forward with information during such investigations. The number and identity of other possible whistleblowers being interviewed in the 787 case remained unclear.