Federal prosecutors from Boston have interviewed people in Los Angeles this week, asking about additional students whose parents have not been charged in the college admissions scandal, people familiar with the matter told The Times.

The prosecutors, led by Assistant U.S. Atty. Eric Rosen, are interviewing potential witnesses in Los Angeles to bolster their existing cases and build new ones against people who have not yet been charged, according to two sources, who requested anonymity because they were not authorized to discuss the talks publicly.

In a court filing earlier this month, Rosen said his team of prosecutors would be traveling “for business” the week of April 15-19.

Fifty people, including 33 parents, have been charged in the investigation so far. While many of the defendants hail from California, the investigation was handled by the Massachusetts U.S. attorney’s office, which learned of the scheme while investigating an unrelated securities fraud case.

Prosecutors indicated in a recent court filing that they’ve collected evidence that can be used to charge additional people. In a request for a protective order on evidence that will soon be turned over to defense attorneys, they said the wiretaps, financial documents, emails and surveillance photographs contain information about “targets of the investigation who have not yet been publicly charged.”

A Bay Area couple have signed formal cooperation deals with prosecutors. Bruce and Davina Isackson of Hillsborough are accused of paying $600,000 to rig a college entrance exam and slip their two daughters into UCLA and USC as recruited athletes.

Prosecutors want to know whether anyone at UCLA or USC knew about the athletic recruiting scheme beyond the coaches and officials who have already been indicted, a person familiar with the matter said.

Prosecutors in Boston have secured guilty pleas or agreements to plead guilty from 18 of the 50 people charged last month, including a guilty plea from the scheme’s mastermind, Newport Beach college consultant William “Rick” Singer.

Thirteen parents and one University of Texas tennis coach agreed to plead guilty earlier this month. Among them was the actress Felicity Huffman, who said in a statement she was ashamed and remorseful at having committed “a transgression” toward her daughter and the public. Huffman is accused of paying $15,000 for Singer’s accomplice to fix her daughter’s answers on the SAT. Huffman maintains her daughter knew nothing of the scheme.

The day after Huffman and 13 others said they would plead guilty, 16 parents — including the actress Lori Loughlin and her husband, J. Mossimo Giannulli — were indicted by a grand jury in Massachusetts and saddled with an additional charge of money laundering conspiracy.

All 16 have said they will plead not guilty.