Unforgotten series 2 episode 1 recap: who killed David Walker? Crime drama theories examined. ITV, ABC and BBC First in Australia

What do we know so far about David Walker’s murder?

Well, we know he was stabbed, possibly through the heart, with what the team’s pathologist, Amy East, thinks was a kitchen knife.

And we know he was dumped in the river in and around 1990, not long after he’d been reported missing by his wife.

Then there’s his pager: we know he had it on him when he was dumped in the water – and that tech expert Nathan is going to be able to glean some clues from it now that he’s managed to bring it back to life.

And to think, the duo were able to find out all this thanks to a watch that had been recently repaired…

Who killed David Walker?

We’ve now met our four suspects and each of them seems to have hinted that they’re capable of anything.

DSI Tessa Nixon, who was married to Walker when he disappeared, is devastated to learn of his death – but is her anguish genuine? She assumes he took his own life because he'd been depressed at the time, but Cassie mentions that the DSI would know how to fake a reaction. After all, Nixon herself points out that 63 per cent of murder victims are killed by the partners. Could she be responsible?

Then there’s highly-respected defence barrister Colin Osborne, who has no apparent connection to the victim but has shown he can be vengeful. He suffered homophobic abuse in a supermarket before keying the offender’s car, and then found himself backed into a corner by the man who’d seen the whole thing. Could his temper have flared previously?

Next up is teacher and Sixth Form head Sara Mahmoud, who is discussing why women kill with her class when we first meet her. Her talk about whether Lady Macbeth could be more evil than her husband seems almost too obvious, but could it be the hint that she’s the culprit?

And finally there’s nurse Marion Kelsey, who despite her best intentions seems to walk a blurred line. She’s shown herself to have the capacity to fly off the handle as her frustrations with her sister, Elise, bubble over. Elise mentions that Marion was nowhere to be found for about “ten years”. Could she have known David Walker during that time? And could she have killed him?

The answers we need could well be hidden on the pager Nathan seems to have revived, but we’ll have to wait until next week to find out who they’ll take us one step closer to…

Why is Jason Walker lying to his mum?

On a side note, Jason seems to be telling some right porky pies to his mum. He told her he'd had a big party and that his neighbours had been the last to leave, but when he went home his flat was perfectly tidy, his neighbour apologised about not coming, and the only birthday card he'd had (aside from his mum's) was from the local Chinese takeaway.

What's up with the young man? And how will he take the news of his father's murder?

What does Tyler really want from Colin and Simon?

He claims to be the partner of Flo's birth mother and says the pair just want some money so they can set up a new home in Hastings. But is he telling the truth? And if that's all they want, why is he blackmailing Colin?