SAN PABLO -- A 55-year-old San Pablo man was fatally shot in front of his 5-year-old son at a gas station Saturday night, police said.

Police found Rodrigo Martinez shot several times and slumped in his vehicle at a Shell station in the 2800 block of El Portal Drive about 11:15 p.m., San Pablo police Cmdr. Jeff Palmieri said. Officers discovered his young son in the car with him, physically uninjured but traumatized by the event.

"We don't know if the people who committed this heinous act knew there was a 5-year-old in the car," Palmieri said. "We're very happy the child was not hurt, but it is very traumatic with him being 5 years old and not being able to tell us much besides what we already knew."

An ambulance took Martinez to a hospital where he was pronounced dead, Palmieri said. The young boy was turned over to his mother at the scene.

Palmieri said that the man and his young son were sitting in a parking space at the time of the shooting, and had not been pumping gas. Investigators did not immediately know why the pair were at the gas station, nor where they were headed.

According to Palmieri, Martinez did not have a permanent residence and appeared to be homeless. It was unknown if his young child, who was in his custody at the time of the killing, was also floating from place to place.

No suspects have been identified in the shooting, Palmieri said. Investigators are still searching for a motive, and do not know if the shooting was narcotics-related or perhaps a botched robbery.

The homicide was the second in the city in less than a week. Richmond resident Franklin Lopez-Guardado, 19, died in a shooting in the 2100 block of Dover Avenue last Thursday. No arrests have been announced in that case, though two younger males were seen running from the scene, Palmieri said.

Palmieri said investigators are looking into whether the two killings may be related. Physical evidence collected from both scenes are being compared to see if anything matches, he said.

The slayings were the first in more than a year in the city -- San Pablo recorded no homicides in 2013. Authorities asked anyone with information about either killing to contact investigators at 510-215-3150.

"The fact that we had two homicides in a week is obviously tragic," Palmieri said. "I do know for a fact there will be some closure eventually -- we're going to solve this. Between us and the community, that's what we do."

Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.