Well, that's the kind way to put it. Sometimes... not always, thank goodness... LE develops tunnel vision and make up their minds right off the bat that the parents are responsible. A few of them are just downright lazy and won't investigate any other possibility. Maybe the parents didn't buckle under the pressure or didn't react the way they thought they should, so they hammered at them and lied to them to get them to crack. Sometimes it works, sometimes it doesn't. But it's not always just to clear the family, once in a while they find out months or years later, they were wrong. The case of Riley Fox is one good example. They beat a confession out of Kevin Fox and he had nothing to do with it. ("Beat" is a figure of speech, btw.) Sometimes, in some cases, they simply want somebody to pin it on because unsolved cases don't look good when it's time for an election. The sheriff and the DA are elected officials, and they want to look like they're doing their jobs.
They can lie all they want to while the investigation is ongoing but they CANNOT lie once they get to court. If they told the parents that they had proof, or physical evidence that tied them to the crime, and they get a confession out of them, they better be able to produce that evidence, because if that was the basis for getting an arrest warrant and an indictment and it later comes out in trial that there was no such evidence at the time of that confession... their case is down the drain. A good defense lawyer can get that confession thrown out and convince a jury that it was coerced by LE, or that the evidence did not exist at all and therefore not admissible.
So, that lying to the family can work both ways, it can sometimes come back and bite them in the butt.
