Neither Feinberg nor a spokesperson for the DA's office could immediately say how many cases were reviewed, although Feinberg said the review likely involved fewer than 500.
Feinberg said cases were reviewed to determine whether Castillo's testimony was independently corroborated by other evidence or testimony.
The cases to be dismissed include two 2016 misdemeanor convictions for reckless driving, according to the DA's office. A felony conviction for resisting arrest, which will also be dismissed, appears to have been from 2005. A spokesman for the DA’s office wrote that the case was "too old" to provide charging documents.
"This is not to say that these three people weren't actually guilty of the crimes," Feinberg said. "But it's just that based on what we know now about Detective Castillo, without any sort of independent corroboration, the interests of justice are best served by moving to dismiss those counts."
Defense attorneys in more serious cases Castillo was involved in may very well have a different interpretation of the weight of evidence he provided, Feinberg said.
"We welcome any additional requests for review," he said.
The Contra Costa Public Defender's Office did not immediately respond to request for comment.
Becton created the DA’s conviction integrity unit in May, about a month after Castillo's misconduct came to light.
"A prior conviction with any impropriety causes a great disservice to our system," Becton said in a written statement on the pending dismissals. "We will continue to review prior cases and conduct investigations as appropriate."
The DA is not independently seeking misconduct records about other police officers and sheriff's deputies who may have provided similarly tainted testimony, a spokesman confirmed.
The office is, however, encouraging members of the public to contact its conviction integrity unit with any information about Castillo.
This story was produced by the California Reporting Project, a coalition of 40 news organizations across the state. The project was formed to request and report on previously secret records of police misconduct and use of force in California.