The family of a woman in China who died while reportedly answering her iPhone say her body showed signs of electrocution, and they want answers.

Ma Ailun was charging her phone–which she bought at an official Apple store in China–last week when she received a call and answered it with the charger plugged in. She allegedly received a shock so great that her heart stopped, but officials are investigating the cause and haven’t released details yet.

Someone claiming to be Ma’s sister posted on Weibo–a Twitter-like site–about the incident, saying she wants not just an explanation, but a warning to users so this doesn’t happen again.

“(I) hope that Apple Inc. can give us an explanation. I also hope that all of you will refrain from using your mobile devices while charging,” the post read.

Apple released a statement, saying they intend to launch a full investigation into the matter. Experts say that a cell phone couldn’t emit enough voltage to kill someone unless the charger was damaged in some way.

“We are deeply saddened to learn of this tragic incident and offer our condolences to the Ma family. We will fully investigate and cooperate with authorities in this matter.”

A couple of years ago, Apple received reports of iPhones that were “exploding” spontaneously; three users from Australia, France and Brazil all claimed that their devices started to smoke and emit sparks, and the faces of each phone were destroyed. There was speculation that the battery may have had something to do with the incidents.