Tesla Motors CEO Elon Musk, under pressure after a fatal crash involving one of his electric cars, went on Twitter Sunday to say he's working on another "Top Secret Tesla Masterplan." Musk said he hoped to publish details this week. We are learning that Apple could be related to the plan, but please consider this information solely as an unconfirmed rumor.

The message echoes an August 2006 blog post, titled "The Secret Tesla Motors Master Plan," in which Musk unveiled the cars that became the Tesla Model S four-door family car and the Tesla 3 sports sedan.

Federal officials are investigating a May 7 crash in Florida that killed a man after his Model S's cameras failed to detect a turning tractor-trailer and did not automatically activate the brakes.

Tesla also said last week that shipments to customers fell in the past three months, making it unlikely the California-based firm would meet expectations for delivering 80,000 to 90,000 vehicles this year.