US declines to furnish records and Polanski walks

from a New York Times account:

The director [Roman Polanski] fled on the eve of sentencing in California because of fear that the presiding intended to renege what his defense lawyers said was a deal to avoid a prison sentence.

Ms. Widmer-Schlumpf said the American authorities had rejected a request by her ministry for records of a hearing by the prosecutor in the case, Roger Gunson, in January 2010, which should have established whether the judge who tried the case in 1977 had assured Mr. Polanski that time he spent in a psychiatric unit would constitute the whole of the period of imprisonment he would serve.

Details of settlements and agreements can be very sketchy, including in patent law. Here, however, the Polanski's people would have needed to establish that the deal was in fact made. One wonders why the records weren't furnished?