Capital punishment is often opposed on the grounds that innocent people will inevitably be convicted. This fact is well supported in the US. Between 1973 and 2005, 123 people in 25 states were released from death row when new evidence of their innocence emerged. However, statistics likely understate the actual problem of wrongful convictions because once an execution has occurred there is often insufficient motivation and finance to keep a case open, and it becomes unlikely at that point that the miscarriage of justice will ever be exposed.
Another issue is the quality of the defense in a case where the accused has a public defender. The competence of the defense attorney "is a better predictor of whether or not someone will be sentenced to death than the facts of the crime".
Also, improper procedure may result in unfair executions. For example, Amnesty International argues that, in Singapore, "the Misuse of Drugs Act contains a series of presumptions which shift the burden of proof from the prosecution to the accused. This conflicts with the universally guaranteed right to be presumed innocent until proven guilty". However, this refers to a situation when someone is being caught with drugs. In this situation, in almost any jurisdiction, the prosecution has a prima facie case. It may be possible to argue that the standard of proof should be raised to higher standard in case of the death penalty trial. However, many dispute the assertion that this falls under the definition of "improper procedure".