The toddler died after accidentally ingesting fentanyl, which O'Neil had also consumed. He later died at the hospital.
RELATED: 13-month-old baby found dead in Santa Rosa home, police say drugs involved
US Attorney David Anderson announced that three alleged drug dealers have been arrested.
"The defendants are charged with the distribution of fentanyl resulting in death," Anderson said.
Federal agents were even able to trace the origins of the drugs that killed the two to an open air drug market in San Francisco's Tenderloin neighborhood.
[Ads /]
"The Tenderloin has tentacles that extend far beyond its 40 to 50 square blocks in San Francisco," added Acting DEA Special Agent in charge Curt Fallin.
In August, the US Attorney announced a federal initiative to crack down on drug trade in the Tenderloin.
RELATED: Feds announce major crackdown on drug dealing, other crimes in Tenderloin District of San Francisco
15 federal law enforcement agencies partnered with an equal number of federal prosecutors executing arrests in the neighborhood.
In a letter to Supervisor Matt Haney, who represents the district, Anderson said since August, they've made more than 100 arrests and 46 have already pled guilty.
But Anderson also pointed out that there's been a lack of collaboration with local authorities because of the city's broad interpretation of its sanctuary policy partly to blame
[Ads /]
"The way those policies are applied in San Francisco is also resulting in sanctuary indeed and in some instances perhaps immunity for those engaged in criminal misconduct,"
RELATED: RELATED: Man arrested for murder after baby found dead in Santa Rosa home
Mayor London Breed says she's open to working with Anderson.
"Crime happens no matter what and so to attribute it to a policy is, I think unfair," Breed said.
Anderson also said he wishes San Francisco would be a signatory to the Joint Terrorisom Task Force, which the city opted out of years ago.
[Ads /]
So far, its a dead issue with the San Francisco Police Commission, which would decide whether or not to re-join. There is no pending action on its agenda.
Take a look at all of ABC7's Building a Better Bay Area stories and videos.