F.D.A. investigators work with grand juries and use subpoenas.
That tactic allows it to use subpoenas and other techniques to try to identify the senders.
On the issue of sealed settlements, Mr. Jeffers said that investigators and regulators could use subpoenas if they really wanted access to the information.
Still, that analysis may generally be performed without a wholesale sweep of call records, since investigators can instead use subpoenas to obtain relevant logs from telephone companies.
"The Government will be able to use subpoenas to acquire records in the overwhelming majority of investigations.
Investigators say they are sometimes loath to use subpoenas for the very reason highlighted in Norris' letter-fear of tipping off targets.
Nunes welcomed other Trump associates to come forward but was evasive about whether he would use subpoenas to call in witnesses who did not volunteer ― an authority Schiff has said the chairman must be willing to exercise.
For these reasons, two laws, one federal and the other a California statute, require prosecutors to use subpoenas, rather than a warrant, to obtain information from journalists in criminal investigations.
The chairman and vice chairman have compiled a list of 20 individuals they plan to interview and have scheduled times for five, they said, and are willing to use subpoenas to bring in unwilling individuals if necessary.
Investigators never used subpoena powers to obtain information, but rather "relied on information voluntarily produced by Mr. Madoff and his firm," Mr. Cox said.
"In seeking documents and testimony from public agencies and from companies, the commission has made it very clear that it is committed to using subpoena power if there is a lack of, or delay in, compliance," Mr. Angelides said.
