The favorite technique of the FBI when trying to get a conviction is to try to turn someone lower in the food chain against the defendant. You are probably most familiar with it in investigations of organized crime in which an under boss is pressured to testify against a boss in return for leniency. That is exactly what happened in the case I discussed above. The FBI offered a manager a break in return for his testimony against the defendant. In return the manager was required to plead guilty to one felony count, no fine and no prison term.  However, he now has a criminal record.

Generally the FBI is not required to inform you of your right to legal counsel until they take you into custody.  However, I have read cases in which the court ruled that custody does not necessarily mean arrest, but also situations in which the individual's freedom is restrained. The problem arises that before they take you into custody they may interview you several times, and then arrest you on the basis of your prior statements while not being represented by an attorney. At that point your goose is cooked. That is why you always ask if you are the target of the investigation before answering any questions. Generally it is a good idea never to answer their questions without your attorney present.

Unfortunately, it has been my experience that during the investigative process little distinction seems to be made between potential defendants and potential witnesses who have done nothing wrong. If anyone is hurt in the process...too bad justice is done as far as they are concerned. The same approach cited in your article seems to be routinely used ...a veiled threat of possible indictment...allegations that the defendant is guilty of some crime with which the witness could be implicated (the FBI and U. S. Attorneys  have immunity so they can say pretty much anything they like with no fear of litigation)...and then throw the witness a bone to create the impression that they will go easy on him.

In the case I cited I can recall the indictment process. Employees of the defendant were interrogated before a grand jury. One of the jurors asked if the witness knew that the defendant was engaged in illegal activity. The juror seemed to forget that one is innocent until proved guilty, but the prosecutor did nothing to restraint the questioning.

In the case I mentioned above they interviewed one of the defendant's accountants prior to trial. The accountant later testified as a defense witness at trial. The testimony hurt the prosecution's case. I was later told that the FBI contacted him , and told him..."We don't think you told the truth during the interview." In other words there was a suggestion of a potential indictment for obstruction of justice. Fortunately, the accountant did not have to testify again after that, and the FBI let it die. Makes one wonder how strong the obstruction of justice case would have been.