Cash App founder Bob Lee argued with suspect before his murder - prosecutors

Cash App founder Bob Lee was stabbed to death in San Francisco on 4 April

Cash App founder Bob Lee was stabbed to death after an argument over the sister of the suspect charged in his killing, prosecutors say.

Tech executive Nima Momeni, 38, has been charged with murder.

A witness told police that Mr Momeni questioned Mr Lee about his sister the night before the stabbing, according to court documents.

Mr Lee was found unconscious on a San Francisco street early the next morning of 4 April and later died.

Prosecutors called Mr Lee's killing a "planned and deliberate attack" in court documents. They set out the timeline of events that led to his death.

The witness, Mr Lee, and Mr Momeni's sister Khazar Elyassnia were drinking with friends at an apartment on the afternoon of 3 April. Mr Momeni confronted Mr Lee about his relationship with Mrs Elyassnia, the witness said.

He questioned Mr Lee about whether his sister was "doing drugs or anything inappropriate", prosecutors said. Mr Lee "had to reassure [Mr Momeni] nothing inappropriate happened".

Mrs Elyassnia is married to a prominent plastic surgeon in the Bay Area; the witness said they did not know the nature of the relationship between her and Mr Lee.

Investigators discovered a text message from Mrs Elyassnia to Mr Lee following the exchange.

"Just wanted to make sure your doing ok", the message read. "Cause I know my nima came down wayyyyyyy hard on you. And thank you for being such a classy man handling it with class."

Shortly after midnight, Mr Lee went to Mrs Elyassnia's apartment. Mr Momeni was already there; CCTV shows Mr Lee and Mr Momeni leaving together in Mr Momeni's BMW about a half hour before the murder.

Prosecutors claim Mr Momeni drove to a secluded area where he stabbed Mr Lee with a kitchen knife.

Mr Momeni, founder of a software company called Expand IT, made his first court appearance on Friday and was ordered held without bail until his arraignment on 25 April. Mr Momeni's sister and her husband also attended.