Absolute Immunity on Trial

'Under federal law, only a federal prosecutor, and not a federal police investigator, can gauge whether information offered by a jailhouse snitch is useful enough to offer time off the informant's sentence in exchange for his testimony. That means prosecutors are put in the role of interviewing potential informants to determine whether the stories are plausible (or, if they're less scrupulous, merely whose stories are most damaging to the defendant).'