Similarly, fiber analysis has proven unreliable. Last year, the FBI claimed fiber analysis implicated a group of drug users in three murders at Yosemite National Park. A hotel handyman's subsequent confession to the murders revealed the unreliability of that evidence. So far as I know, no one has been wrongly convicted as a result of the defense's use of junk science. One recurring theme in cases in which an innocent person is sentenced to death is the jailhouse informant who testifies that the defendant confessed to the crime.
Jailhouse informants have an agenda.
They are looking for a way to lessen their own punishment and are willing to say anything to help themselves. When one considers the fact that these are jail inmates, it should hardly be surprising that they regularly prove to be dishonest. Jailhouse informants are not normally defense witnesses. They testify for the prosecution to obtain shorter sentences or get charges dropped. The defense is not allowed to reward witnesses.