Investigators say the little boy accidentally shot himself on Saturday.
Jace Alexander's dad came home from work to a nightmare. He'd left his 2-year-old son in his northwest Fresno home that morning with his fiancée and their roommate, Oscar Ramos.
A couple hours later, the two adults heard a pop in a different room.
"They immediately ran towards the bedroom where Jace stays and they saw Jace lying on the floor in a pool of blood and there was a gun lying next to Jace on the bed," Fresno Police Chief Jerry Dyer said.
The Sig Sauer handgun belonged to Ramos and he actually had a safe for storing it. But Dyer said Jace's dad had found the loaded gun unsecured in the house earlier the same week.
"He gave that gun back to Oscar and said, 'Do not leave that handgun in locations in this house that can be accessed by my children,'" Dyer said.
WATCH: Chief Jerry Dyer's news conference on shooting
Jace had two siblings, but on Saturday, he was the only child in the home. Police said Jonathan Alexander and the mother share custody.
"Prior to the incident, she had picked up two of the three children and left Jace with dad one more day," said Fresno Police Det. Robert Holguin.
Police said Ramos paced the house for five or 10 minutes without calling 911 before the father's fiancée grabbed his phone and called for help.
They said the extra time probably wasn't enough to save Jace, considering the wound.
Investigators said Ramos took full responsibility for Jace's death and they booked him on charges of criminal storage of a firearm and child endangerment.
Dyer said he hopes the boy's death serves as a reminder to gun owners to keep their weapons secure. "Children have no idea when they come across a firearm like this whether it's real, a toy, or what the potential there is for that gun to cause death," he said.
Since 2011, Jace is at least the third child to die in Fresno because of an accidental shooting where a child pulled the trigger.