Bob Lee, a well-known tech executive who founded Cash App and served as the Chief Technology Officer of Square, was fatally stabbed outside of downtown San Francisco early Tuesday morning. Lee, who was 43 years old, was transported to a local hospital with life-threatening injuries but succumbed to his injuries before reaching the hospital, according to the San Francisco Police Department. Although the medical examiner has not yet identified the victim, sources have named Lee as the stabbing victim. Police have not released the names of any suspects or made any arrests, but Lee's death is now being investigated by the San Francisco Police Department's Homicide Detail. Lee's colleagues took to social media to pay tribute to him, with the CEO of MobileCoin, where Lee had been serving as Chief Product Officer, calling him an "incredible human being" and "a force of nature." Lee was also the founder of Moby App, a privacy-protecting wallet for the 21st century. The police have asked anyone with information about the fatal stabbing to call their tip line.