At about 1 a.m. California time in 2013, a scientist emailed Apple Chief Executive Officer Tim Cook with an irresistible pitch.

"I strongly believe that we can develop the new wave of technology that will make Apple the No. 1 brand in the medical, fitness and wellness market,” he wrote in the email, which was later included in legal documents. Some 10 hours after the message was sent, an Apple recruiter was in touch. And just weeks after that, the engineer was working at the tech company on a smartwatch with health sensors.

A flurry of activity began. Within a few months at Apple, the employee asked the company to file about a dozen patents related to sensors and algorithms for determining a person’s blood-oxygen level from a wearable device. But this wasn’t just any engineer. He had been the chief technical officer of Cercacor Laboratories, the sister company of California-based Masimo, which went on to get to the U.S. to ban the Apple Watch.