A series of rooftop blazes at Walmart stores in recent years left the retail giant with a pressing question: What was causing all the fires?

In a lawsuit filed in New York State Supreme Court on Tuesday, Walmart proposed an explanation. “The answer was obvious and startling,” the complaint said. “The stores all had Tesla solar panels installed by Tesla on their roofs.”

Walmart is suing Tesla for breach of contract, contending that at least seven rooftop fires at the retailer’s stores between 2012 and 2018 were a result of problems with solar panels installed by the company.

The complaint asserted that Tesla engaged in “widespread, systemic negligence” and “failed to abide by prudent industry practices in installing, operating and maintaining its solar systems.” It said the panels were installed on the roofs of more than 200 of the 5,000 Walmart locations in the United States.