A jury was being chosen for a murder trial nearly three decades ago in California. The state was seeking a death sentence for Ernest Dykes, who had been charged with killing a 9-year-old boy during a robbery in Oakland.

Weighing who should be struck from the jury pool and who should be kept, a prosecutor made notes about a prospective juror:

“I liked him better than any other Jew but no way.”

Other notes about prospective jurors bore evidence of similar prejudice:

“Banker. Jew?” read one.

“Jew? Yes,” read another.

The notes — just handwritten scribbles — were discovered recently in an internal case file from the 1990s when Mr. Sykes was convicted of murder and sent to death row. A federal judge who is weighing an appeal by Mr. Sykes told the Alameda County District Attorney’s office to conduct a top-to-bottom search for any additional documents, and that search turned up the notes, which are now in the hands of the judge.

The notes offered a startling glimpse into a practice that some defense lawyers long suspected was going on, and that a former prosecutor had alleged was common in Alameda County — prosecutors seeking to exclude people of certain faiths, races or genders.

Now, Mr. Dykes, 51, and perhaps others on death row in California as well, may have their convictions tossed out and be granted new trials. The federal judge weighing his appeal has ordered a review of all California capital cases in which a defendant from Alameda County is still on death row. The county includes Oakland, Berkeley and a host of other Bay Area communities.