The victim and suspect were arguing in a shoe store inside the mall near Interstate Highway 880 around 2:30 p.m., police said.
When the victim left the mall, the suspect followed him outside and fired multiple rounds at him, according to police.
The victim was transported to Eden Medical Center where he was pronounced dead, police said.
The suspect is described as a black man in his 20s and was wearing a green shirt and a gold chain necklace, according to police. He was last seen leaving the mall in a dark green sedan, possibly a Buick or a Pontiac, police said.
Anyone with information about this incident is asked to call the Hayward Police Department at (510) 293-7033. Crime Stoppers of Southern Alameda County is offering a reward of up to $1,000 for information that leads an arrest. Callers can call the Crime Stoppers hotline at (510) 293-7197 and may remain anonymous.