Journalists learn from their first day in the trade that their articles should include the five Ws: who, what, where, when and why. The first four are straightforward enough, objective truths if you like. The fifth, however, often travels into subjective territory. It is frustrated by obfuscation and therefore results in speculation. Sometimes, despite our best efforts, it simply goes unanswered.

Consider three examples. Why were journalists Trevor Birney and Barry McCaffrey arrested? Why did the BBC’s otherwise excellent documentary on Margaret Thatcher omit one of the defining moments in her reign as prime minister? Why do broadcasters go on using vox pops?

In the absence of rational definitive answers to these questions, I will feel free to speculate. You may disagree with my viewpoint, but this exercise is all about showing how difficult it can be to supply the “why” part of our truth-telling journalistic mission.

Why did police really arrest two journalists?

Birney and McCaffrey were arrested in dawn raids in August last year. Their computers, phones and paperwork were confiscated. After the raids, carried out by Durham Constabulary on behalf of the Police Service of Northern Ireland, they were placed on police bail on the grounds they had, allegedly, stolen a confidential document.

The two reporters had obtained – not stolen – that document while helping to make a film, No Stone Unturned, about the murders of six men in a bar in Loughinisland, County Down, in June 1994. Their documentary mounted evidence that the killers, members of a loyalist paramilitary gang, the UVF, had escaped justice because at least one of them was a police informer.

Birney and McCaffrey, in company with the National Union of Journalists, saw this as a gross attack on press freedom. They challenged the legality of the warrants and, thankfully, they were vindicated by two judges in Belfast high court, and then, nine days ago, by Northern Ireland’s lord chief justice, Declan Morgan, who ruled that the pair had acted in a “perfectly proper manner” to protect their sources.

This victory for journalism should be seen in the context of a 48-year history of similar assaults on press freedom by police in Northern Ireland. Judges have repeatedly found in reporters’ favour and against the police where they have been arrested while protecting the confidentiality of their sources.

Given that, why did police trample on the rights of Birney and McCaffrey? There may be some innocent explanation not yet proffered. Otherwise, choose from this list: embarrassment at the failure to arrest the killers named in the film; an attempt to prevent light being shone on the murky business of collusion between police and loyalist murderers; a diversionary tactic to avoid the implications of the message by demonising the messengers. Or, of course, a combination of the above.

Why did the BBC’s Thatcher series ignore the hunger strike?

BBC Two’s supposedly definitive five-part series on the “irresistible rise and dramatic downfall of Margaret Thatcher” has, in the main, been warmly received by critics. “Magisterial”, said the Daily Telegraph’s Asa Bennett. “Outstanding”, trilled Christopher Stevens in the Daily Mail. “Marvellously told and truly historically insightful”, wrote Euan Ferguson in the Observer.

I was enjoying it, too, until I realised the makers of Thatcher: A Very British Revolution, passed 1981 without mentioning an episode that made headlines across the world: her intransigent response to the IRA hunger strike which ended with the deaths of 10 men.

The BBC’s Margaret Thatcher series did not mention her response to the 1981 IRA hunger strikes. Photograph: BBC

Surely everyone remembers the phrase with which she dismissed the men’s demands to be granted political status: “Crime is crime is crime. It is not political, it is crime.”

According to a BBC online article following her death in 2013, it was a defining moment. “To her supporters, it was exactly the kind of uncompromising stand on a matter of principle that made her great. To many in Ireland, it was a display of brutal inflexibility.”

So why the omission? When I asked the BBC, it gave this unconvincing reply: “In five hours of programming, the series aimed to capture as much as possible of Margaret Thatcher’s career, her life and her relationship with her inner circle over the course of 20 years and, as such, difficult editorial decisions had to be made. Unfortunately, this meant that not every event that occurred during Thatcher’s time in power could be included in the final series.”

Really? A statement by the BBC documentary unit’s creative director, Aysha Rafaele, hints at a much more plausible reason. The series is, she said, “a forensic look” at Thatcher’s “impact and legacy on all corners and all aspects of British life.”

Note the “British”. It suggests, yet again, that Northern Ireland is not regarded as truly British.

Why does TV news use so many vox pops?

I now find myself paraphrasing Brenda from Bristol’s reaction to news of the 2017 election: “You’re joking. Not another bloody vox pop. Oh, for God’s sake.” Brenda is the only vox popper ever to make a memorable contribution to such an artless form of newsgathering.

That’s the problem, because reporters bearing microphones, cameras at their shoulder, now haunt the streets of Britain in the hope of finding another Brenda, another piece of comedy gold. After all, it’s about entertaining viewers rather than informing them, is it not?

Brenda from Bristol was horrified that Theresa May called for a snap general election. Photograph: BBC

Ivor Gaber, professor of political journalism at Sussex University and a former TV and radio news broadcaster, believes the overuse of vox pops has reached its apotheosis during the Brexit coverage, which has been skewed heavily towards those opposed to EU membership.

He imagines the thought process of news editors: “Let’s do vox pops in a solid leaver area where we’ll get people to say, ‘Why don’t they just get on with it’. Much better than a remain area where they’re likely to say, ‘Well, on the one hand …’”

I can’t be sure of the political slant because I haven’t studied the output as closely as Gaber. But every time I see a vox pop about any subject, whether on the BBC, ITV or Sky, I know it is not going to reveal anything of any value.

In a piece defending the practice, Mark Easton, the BBC’s home affairs editor, argued that vox pops are “a vital ingredient in trying to understand Britain”.

Sorry Mark, that just isn’t so. If you want to be sure, why not go into the street and ask people if vox pops help them understand anything? But please don’t broadcast the result.