Julian was brought to San Francisco General Hospital by his mother and another family member around 12:30 a.m. Tuesday, police said. He was pronounced dead at the hospital.
Investigators have not determined the cause of the death or released any information about why it is considered suspicious.
The car used to take Julian to the hospital has been confiscated as part of the investigation, Shyy said.
Police have also searched the house the baby was at in the first block of Monterey Boulevard, and have interviewed family members.
As of Thursday morning, no arrest had been made in connection with the death, Shyy said.