A more thorough explanation:

In a criminal trial, tainted evidence refers to evidence that was obtained illegally. For example, if the police gather evidence using a wiretap without a proper warrant, the evidence will be considered tainted. This means that it cannot be used in court to support a conviction.

However, there are some exceptions to this rule. For instance, if the tainted evidence was obtained from an independent source, it may be admissible in court. Additionally, a conviction may still be upheld if it can be shown that the evidence would have inevitably been found by lawful means, or if the tainted evidence was deemed harmless.

For example, if a defendant is accused of murder and the police illegally obtain a confession, the resulting conviction may still be upheld if it can be shown that the evidence would have been discovered through other means. Alternatively, if the prosecution can demonstrate that the tainted evidence was not necessary to secure a conviction, the conviction may still stand.

It is important to note that the use of tainted evidence is highly controversial, as it raises questions about the fairness of the criminal justice system. As a result, courts are often reluctant to admit such evidence, and will only do so in exceptional circumstances.