Bob Lee was part of the tech establishment. The former chief technical officer of Square and founder of the $40bn payment app Cash App.
Ednews reports citing US Daily that in the early hours of Tuesday morning, he was killed in a stabbing, in a supposedly "safe" part of San Francisco.
His death has sent a chill through the tech community.
Twitter's former CEO, Jack Dorsey, called the killing heart-breaking.
His friend and fellow tech founder Joshua Goldbard tweeted: "Bob was like a brother to me… Bob's energy was infectious. He made friends everywhere he went."
Elon Musk also added his thoughts on the killing.
"Very sorry to hear that. Many people I know have been severely assaulted. Violent crime in SF is horrific."