There is a very famous case in The Netherlands where two men claimed to have witnessed two of their friends rape and murder a woman. DNA evidence was collected from the body of the victim, which didn't match either of the men. The prosecution argued that the victim had had consensual sex with an unknown man some time before the crime. The men were convicted, but eventually the case was thrown out and they were released after having spent years in prison.Not saying this is what happened in the case you describe, but confessions are in general not robust evidence; nor, in general, are eyewitnesses.
Eventually the DNA sample was matched to the actual perpetrator, who had actually been questioned in the immediate aftermath and had refused to give a DNA sample at the time. He was matched because he had been forced to give up a DNA sample after being convicted of abusing his girlfriend.
So yeah, eyewitness testimonies can be pretty questionable, even when the perpetrators aren't strangers to the eyewitnesses and misidentification would seem impossible. And DNA evidence can apparently be explained away if LE is exceptionally motivated.