(AP) — Authorities in Connecticut have launched a criminal investigation into the cause of an explosion that killed five people at a power plant under construction, saying they can't rule out negligence.

Middletown Mayor Sebastian Giuliano (joo-lee-AH'-noh) says if everything had gone right at the Kleen Energy plant on Sunday, there wouldn't have been an explosion. He says there's a point at which negligence rises to the level of criminal conduct and that's what's being investigated.

It's unknown what caused the blast. Police Acting Chief Patrick McMahon says police have ruled out any intentional act and are focusing on whether there was negligence while workers were clearing gas lines of air.

Officials representing the workers and a private equity fund that owns a majority share of the power plant haven't commented.

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