Apple is being sued over a fatal car crash in which a driver was distracted by FaceTime. The plaintiffs allege it failed to introduce technology it had a patent for that could potentially have prevented the driver from using the app.

The case, filed in a Californian court in early December, relates to a road accident in Texas that happened on Christmas Eve, 2014.

The driver, "distracted while using the 'FaceTime' application on an iPhone 6 Plus during the operation of his motor vehicle," crashed at 65 mph into the back of a vehicle that was stationary due to traffic, the court documents say. (We first saw the case over on Apple Insider, and you can read the full filing below.)

Inside the car were Bethany and James Modisette, and their two children — Isabella and Moriah. The family sustained serious injuries, and Moriah died of her injuries in hospital. She was five years old at the time.

It's a tragic case — but why is Apple involved? The company is being sued because, the Modisette's lawyers claim, it has technology that could have prevented it but failed to implement it.

The court filings point to a patent that Apple applied for in 2008 (and was granted in 2014) that would "lock out the ability of drivers to use the 'FaceTime' application on the Apple iPhone while using a motor vehicle."

The case alleges that by failing to incorporate this patent, Apple contributed to the death of Moriah and the injuries of the rest of the family.

The company's "failure to design, manufacture, and sell the iPhone 6 Plus with the patented, safer, alternative design technology already available to it ... and failure to warn users that the product was likely to be dangerous when used or misused in a reasonably foreseeable manner ... rendered the Apple iPhone 6 defective when it left defendant APPLE INC.'s possession, and were therefore a substantial factor in causing plaintiffs' injuries and the decedent's death," the Modisettes' lawyers allege.

An Apple spokesperson did not immediately respond to a request for comment.

Here's the full court filing: