This post, and many others like this, assume that there are a number of police who know the "truth" and simply remain silent. That is not a skeptic position.
I don't think the post assumes anything of the sort.
What seems to be common to all these cases, and this one is hardly unique, is that the investigators are irrationally convinced they have the right culprit,
in the teeth of the evidence.
An interesting example is the first defendants who were tried for the murder of Damilola Taylor. The police went flat out after them trying to build a case, even though they had an alibi. They were convinced the alibi was breakable, and brought them to court on the basis of the contention that they could have run from the scene, the very second Damilola was stabbed, and reached the spot where their mobile phones had connected to a transmitter within a couple of minutes.
This would have had to assume they were excellent prospects for the next Olympics. It also presumed that they were bright enough to take off the very second they realised the boy was stabbed, without hanging around for a second, and that they knew there was a particular place they could reach that would give them an alibi through mobile phone masts.
The police bought it to a man. They bought it to the point that they started grooming a witness, a teenage girl from a poor background, putting her up in an expensive hotel with room service on tap to encourage her to get her statement right.
Fortunately the jury didn't buy it. There was tabloid outrage at the time, that these killer lowlives had gone free.
But then someone looked again at the evidence, found some quite obvious bloodstains that had been overlooked by forensics the first time round, got them tested, and hey presto the true culprits were traced, prosecuted and convicted.
Was there a "conspiracy" to accuse the first bunch of suspects, with a number of police who knew the truth and remained silent? No. They were "married to the vein", and genuinely believed these people were guilty in spite of the evidence.
I see no reason to assume that this case is any different.
Rolfe.
ETA: I should say that in the Taylor case, the reason the jury didn't buy it wasn't apparently because they didn't think the sprinting-for-an-alibi story wasn't credible, but because the police handling of the teenage "star witness" became public and was much criticised. The news about her behaviour at the plush hotel, and the way she seemed to be milking the situation for favours, led to her testimony being discredited. If that hadn't happened, it's likely the first defendants would have been convicted, and nobody would ever have re-examined the evidence and found that bloodstain.