I want to write a murder mystery. I'm picturing a six-part miniseries.
There are a bunch of suspects early on, mostly from one single family. Maybe there was an old-fashioned feud with the victim's family, maybe there was a business deal gone bad, but either way, people were at each others' throats figuratively before it was literal.
In the second episode/part/whatever, there's a red herring, probably some action as the police try to apprehend someone, but ultimately they arrest the killer and get him in custody. (Gender isn't set in stone yet.) After this point the police are mostly doing procedural work, but not actually looking for clues or arguing with witnesses with questionable alibis across a table.
The third and fourth episodes focus on the fallout. The killer's dad doesn't believe his son is guilty, mom believes he did do it and is glad, big sister has an agenda of her own and is keeping some secrets. The victim's family is torn apart. They're grieving, and not always in healthy ways. The police investigation revealed a skeleton in their closet or two. Some may even try to get vengeful. Then there's the red herring. His name was dragged through the mud by the media. He's a pariah. His life and business are ruined. He might eventually turn up dead - and whose fault is that?
The fifth episode introduces some concern that the police might have got the wrong guy or screwed up the evidence in a way that makes the case fall apart. If they got the wrong guy, who's the real killer? And is he likely to try again? In addition, the police also realize that the victim had a lover no one knew about who's still out there. Who is it? What's their agenda?
In the climax, the police and the few trustworthy members of the families have to find out who the victim's lover was to stop them from taking revenge and more! Along the way, the concern about the original case is resolved neatly - additional evidence is found, they really did get the right guy.
I enjoyed Broadchurch, but it shared a problem with most of its genre: you can safely ignore all but the beginning and the end. At least three characters are treated as serious suspects despite the fact that in the end they're completely innocent. More people are involved somehow, but not remotely the way it seems at first. Innocent people knew about the crime before the police, or knew that other suspects were acting suspiciously, and did nothing about it for one contrived reason after another. The detectives allow and writers force this to happen by having everyone mislead or outright lie to the police about embarrassing foibles the police wouldn't remotely care about if they knew. Apparently absolutely everyone would rather be suspected of murder than exposed as having gambling debts, or has done something that sounds like a sex crime if they describe it vaguely enough. This is a tiny bit annoying in hour-long TV shows but really can be a problem for a six-episode miniseries. Broadchurch was six hours long but you only need to see the first and last 10 minutes or so to understand the murder.
Partly, of course, this is a genre convention. In a murder mystery, the whole point of the story is generally the mystery about who committed murder. But watch enough of them that use innocent suspects as a source of drama and it gets annoying.
Broadchurch was a perfect demonstration of why that shouldn't be necessary - the show is only vaguely about whodunnit; it's much more of a soap opera with a lot of secrets and lies in apparently normal families demonstrating how you never really know someone. The death of some kid, and finally catching the killer, is almost a framing device. But there's no reason the writers had to do that.