Authorities said Joseph Ulloa, 22, was shot multiple times at his home in the 1100 block of North Evergreen Street, a known gang area, about 1:30 p.m.
There is no suspect information and detectives do not know the cause of the shooting.
He was alone watching his toddlers at the yard sale. Money appears not to be the reason.
"I know how much he made. He only made 50 cents," said the victim's wife, Monique Ulloa.
Detectives said the shooting doesn't fit the typical profile. A man walked up and held a conversation before he shot him six to eight times.
"It was more of a personal, up-and-close shooting. It wasn't a drive-by. Maybe he knew the suspect," said Det. J.A. Rios of the Los Angeles Police Department.
In his last moments, the young father may have rushed to shield his 3-year-old daughter.
"His hands were holding the screen door shut and my daughter was on the other side witnessing everything," Ulloa said. "He was here with our kids all the time. That's what's important to him. His children."
The victim attended a trade school to become a security guard. He had one misdemeanor on his record.
"I believe it was for a non-drivers license. That is pretty much it. So pretty much nothing," Rios said.
Anyone with information is urged to call LAPD detectives at (323) 342-8958.