Criminals will do anything if it means they are better off as a result, including lying under oath. Firstly, as convicts these people have already proven themselves to have a faulty moral character.  Secondly, defendants have an incentive to shift blame to reduce their own culpability. By incriminating another member of their group, informants are able to tell a story that is favourable to them, lessening their own moral culpability and reducing the cost they have to pay for committing a crime. In order to secure these benefits, cooperating witnesses have every incentive to fabricate evidence. James W. Haldin writes: “An offer of prosecutorial leniency enhances the natural tendency of an accomplice to lie by providing an incentive to offer testimony that is favorable to the prosecution…. the witness must satisfy the prosecutor in order to obtain the benefit of his bargain”[1].  Moreover, it is almost impossible to verify whether or not their information is accurate. Not only do accomplice witnesses have a motive to fabricate, they often have an ability to fabricate and to fabricate convincingly. They can manipulate their version of events without arousing much suspicion as they know all the details of the crime and which aspects of the enterprise are verifiable so where they can risk lying[2].

Testimony-based plea bargaining forces the defendant to make an agreement with the government which can be broken by the prosecutorial team at any time, leaving no check to ensure that basic rights are protected. Pamela Metzger argues "the government is to be the sole judge of whether the defendant has truthfully and completely cooperated. The decision as to whether the cooperation rises to the level of substantial assistance will be left to the sole discretion of the prosecutor's office. Often a cooperation agreement does not specify the extent of the departure the government will request. And, even if it did, that request would not be binding upon the sentencing court. Finally, if the defendant fails to perform under the terms of the agreement, the prosecutor's office retains the right to use the defendant's statements against him at a subsequent prosecution for false statements"¹. Defendants that enter into plea agreements assume a massive risk insofar as their testimony can be deemed insubstantial at any point of time and then used to convict them in a later trial.

¹ Pamela Metzger, "Beyond the bright line: A contemporary right-to-counsel doctrine," in the Northwestern University Law Review, Summer 2003.

Most cases involving plea-bargaining for testimony are crimes of collusion; that is, prosecutors most often strike deals with members of organized crime groups in order to pin down the leader. As such, informants have incentives to lie in order to either improve their own standing in organized crime’s hierarchical structure or to weed out competition. R. Michael Cassidy confirms: “Because the government frequently pursues cooperation by lower echelon criminals against the higher-ups in an organization, some witnesses may view cooperation with the government in a criminal case as a means to reorder a previously hierarchical relationship…. the informant may be manipulating the system for personal or pecuniary gain, such as a desire to take over the joint criminal enterprise for himself or an ally after helping to put the confederate away”[1]. Even if the plea bargain gives accurate information the government should not be helping lower ranking members pursue their own ambitions by using the state.

The practice of plea-bargaining for testimony assumes that the levels of culpability within a group are totally different. In other words, it assumes that some individuals have negligible levels of culpability and so can be bargained with while others are fully responsible and so deserve to be prosecuted to the fullest extent. But, this division is false because it ignores the collective nature of crimes of collusion. Solidarity in the mob and decision-making procedures in a corporation both change individual intentions by creating a group-based context for one’s intentions that is radically different from the context of personal experience outside of the group. As a result the actions cannot be fully explained by reference to the intentions of individual, isolated people. It therefore makes sense to talk, in a limited way, about the collective intent of social groups.[1] So, allowing testimony-based plea-bargaining disproportionately lays blame in the hands of the ringleaders of the organized crime group. Subordinates, by contrast, become witnesses for instead of enemies of the state and get off with extremely light sentences. However, just because individuals are in an authority position does not mean that they are the most responsible for that crime. Morally, there is no distinction between coming up with a crime and carrying it out. In fact, subordinates are often more dangerous because they have shown that they are willing to carry out heinous crimes. Therefore, giving subordinates more lenient sentencing disregards the collective nature of the crime and so de-links culpability and punishment.