The short answer to this question is yes, some evidence of a crime can be excluded at trial.  There are many reasons for suppressing evidence, some based on the rules of evidence and criminal procedure and another being a judge made rule to be discussed here:  The Exclusionary Rule.

The Exclusionary Rule

The Exclusionary Rule is not a constitutional right, but works to protect certain constitutional rights.  This rule operates to prevent the government from using evidence that was obtained in violation of a person’s constitutional rights.  The Fourth Amendment prohibits evidence gained by an illegal search and seizure.  The Fifth Amendment prohibits evidence improperly gained by eliciting self-incriminating statements.  The Sixth Amendment prohibits evidence gained in violation of a person’s right to counsel.  However, this rule does not apply to civil cases.

The reason for the exclusionary rule is to operate as a deterrent for law enforcement against violations of constitutional rights.  Therefore, a court will balance the severity of the violation against the reasonableness of the actions.  The Illinois Code of Criminal Procedure makes evidence admissible when there are “technical irregularities” that don’t substantially affect constitutionally protected rights.

Fruit of the Poisonous Tree Doctrine

The Exclusionary Rule also takes effect when evidence obtained is in connection with a constitutional violation, but not a direct result of it.  This is called the Fruit of the Poisonous Tree doctrine.  There are certain exceptions to this doctrine that could make the evidence admissible even though it came from a violation subject to the Exclusionary Rule.

First is the Independent Source doctrine, which means evidence can be admissible if it is discovered by legal means wholly unrelated to the original constitutional violation.  Another exception is the Inevitable Discovery rule, which states that any illegally obtained evidence can still be admissible if the government can prove that it would have discovered it anyway by independent and lawful means.  Lastly, is the concept of Attenuation, which means that otherwise inadmissible evidence can become admissible if certain factors exist that lessen or attenuate the degree of violation.

Procedural Matters

Even if evidence can be excluded from trial, there are certain instances where the prosecutor may still present it.  Called, “opening the door,” a defendant who takes the stand in his own defense can be impeached by using previously excluded evidence if he brings the topic up in testimony.  This same tactic cannot be used to impeach a defense witness, however.

Before evidence can be excluded, a court must determine whether the person seeking exclusion has the right to bring the claim.  This is an important concept in Fourth Amendment violations because in order to claim a violation of the right to be free from unlawful search and seizure, that person must have been the target of the investigation.  This must be distinguished from a claim brought by someone who is prejudiced by the evidence gathered as a consequence of a search or seizure directed at someone else.  See Jones v. U.S.  An example of this is evidence obtained by a search and seizure of a vehicle not owned by the defendant, but defendant was a passenger in the vehicle.  The passenger defendant would not have standing to contest evidence obtained in the search of the vehicle because the passenger defendant does not have a possessory interest in the vehicle and no right to assert privacy in its interior or compartments.  See Rakas v. Illinois.

There are complex and detailed procedures that must be followed to have evidence suppressed in a criminal trial.  A qualified Illinois Criminal Defense Attorney is your best resource to ensure the greatest protection of the law when navigating the criminal justice system.