This is interesting, and disturbing. The SEC and criminal investigators (FBI/DOJ) are thinking about indicting corporate executives, in this case in connection with backdated options. The investigators interview employees under an immunity grant good only for the day of the interview. The DOJ then indicts the executives.
The executives' lawyers want to depose the witnesses. The witnesses refuse, asserting their 5th Am. right, which they can do because their immunity grant was good only for the day of testimony. So the government gets to examine them and, by limiting the immunity grant, to deny their testimony to the defense. (No lawyer for a witness will advise testimony without some sort of assurance from the government).
Sure there is Jencks and Brady, but this strikes me as just wrong. Why would the government do this? The argument of one of the defendant's lawyers--that the government doesn't want its witnesses to contradict themselves in sworn testimony, thus creating impeachment material that would lower their value at trial--seems plausible to me. Perhaps there is some other explanation, but it is hard to see how this one-day-only immunity makes it more likely that these proceedings will get at the truth.
DM