How did he know Sarah ?
The girl who died in the car crash.
Can't remember if it was mentioned in the movie. Have not seen it in a long time.
I cannot remember, but I'm thinking that it was a random car which had crashed into the water. Smith's character jumped in to save the driver and the girl. I think the drive was already dead. The robot jumps in, sees Smith struggling/drowning. He wanted the robot to save the girl, but the robot chose to save Smith and the girl dies in the car. Thus, Smith has a negative predisposition against robots and has PTSD about the event.
shareYes, I know. But he said she wanted to be a dentist. That means he met her before.
shareI preface, I haven't seen the film in a few years.
As you said, it could be true that he knew her, or what is most likely he became to "know her" by researching her life, her dreams, aspirations, etc.,... after she died while Smith feels guilty for not being able to rescue her.
Smith just had a "case" that went wrong, so he's f-up in the head until he has to solve a murder of a prestigious inventor, by his own invention...
That's my interpretation.