The Suspect ending explained: Catherine McCain's killer revealed

The real murderer – who'd killed not just Catherine McCain (Tara Lee) but also Cara (Bronagh Waugh) and, it transpires, several others – was also unmasked, with DI Ruiz (Shaun Parkes) finally coming to believe Joe's protestations of innocence as the fit-up job arranged by the true killer started to fit together a little too perfectly.

So who was behind the killings? What was their motive? And why did they target Joe? Read on for a full recap of events – including a few questions that were left unanswered.

Who killed Catherine McCain?

The real killer was in fact... DJ, the plumber (Tom McKay).

DJ was revealed to be the older brother of Bobby Morgan (Bobby Schofield) – his full name being David Jean Morgan – who used his position as a plumber to infiltrate the O'Loughlins' home, earn the trust of Joe's wife Julianne (Camilla Beeput) and plant a bomb in their basement. (Rather convenient that the O'Loughlins were suffering from dodgy plumbing, allowing DJ the perfect opportunity to insert himself into their lives...)

As a young teen, DJ was subjected to horrific abuse by his mother – when he fled the family home, Bobby became her next victim, something that had haunted DJ his entire life. In an effort to atone for abandoning his brother, DJ went along with Bobby's horrific plan to frame Joe for Catherine's murder.

DJ was also the mysterious figure who paid £500 to outbid Joe for his daughter's drawing of a whale – it's that same sketch's presence in his family home that first tips off Joe to the plumber's deception – and, presumably, was also paying for Bobby's high-price lawyer. (His plumbing business must be doing well.)

Why was Joe framed?

Though DJ committed the actual killings, explaining how his brother could have an alibi for the killing of both Catherine and Cara, it was Bobby who was the mastermind behind the plot to frame Joe.

Years earlier, Joe made a terrible mistake when he falsely accused Bobby's father of abusing his son – unaware that it was in fact Bobby's mother inflicting the abuse. Lenny Morgan ended up being separated from his son and later took his own life.

Having accessed his social services file, Bobby read up on those involved in his father's case and decided to take revenge. A social worker who pushed through the paperwork saw his daughter poisoned, the wife of the judge who ruled Lenny could no longer see his son was deliberately knocked off her horse and broke her neck, Bobby's psychologist Rupert Erskine was attacked, gagged and left to die of dehydration, and Joe's colleague Melanie (Angela Griffin) lost her partner Boyd in a deliberate traffic collision.

For Joe, who signed the court report on Lenny's case, Bobby planned a different fate – like his father, Joe would be accused of a terrible crime he did not commit and, once he'd suffered enough, would eventually perish in an explosion, hence why DJ planted a bomb in the O'Loughlins' basement.

Having befriended Joe's dad (Dermot Crowley) and learnt all about Dr. O'Loughlin from his chatty father, Bobby decided to murder Catherine – someone that Joe would, in the police's eyes, have a motive to kill, since she falsely accused him of sexual assault – and dumped her body in the cemetery around the time he knew Joe would be visting his mother's grave. (It was almost certainly Bobby who dumped the body, or at least assisted DJ in doing so, given that Joe smelt chloroform on him, the same substance found on Catherine's body.)

Was Jack Owens involved?

Prior to DJ being revealed as Bobby's brother and co-conspirator, Joe suspects that his old friend Dr. Gerald 'Jack' Owens (Adam James) might be the older male figure who was identified as having poisoned the social worker's daughter and who forced the judge's wife off her horse.

In fact, it seems the only thing Jack was really guilty of was lying about his previous romantic association with Catherine McCain. That and harbouring a decades-long crush on Joe's wife Julianne. He might've been a bit of a creep but we hope Jack got an apology from Joe for having served his friend up to the police as chief suspect.

What happened at the end of The Suspect?

The series reached an explosive climax – literally – when DJ's conscience got the better of him and he released a captive Joe and family from their home. DJ returned to the basement and was killed in the resulting fireball, while Bobby escaped but was taken into custody by the police, who no longer suspected Joe of being involved in anything illegal.

The final scenes see Joe continuing to cope with his Parkinson's diagnosis, living in a new home with Julianne and daughter Charlie (Uma Warner). A happy ending? Perhaps, though one that leaves us with a few questions...

Why was Bobby apparently obsessed with the number "21" if it was DJ who committed the murders and somehow made Catherine stab herself that many times? Was he just taunting Joe with the number during their sessions, knowing what his brother had done and the fate that was about to befall the psychologist?

And what happened to Bobby on Waterloo Bridge, where he was found by police, anxious and badly beaten, in episode two? Was this also somehow part of his plan? It's hard to imagine DJ harming his brother...

Ah well – maybe we should be more like DI Ruiz and stop expecting everything to fit together quite so neatly.

Read more about The Suspect:

• Aidan Turner on The Suspect and whether to expect any more Poldark
• The Suspect director reveals how they filmed tense opening scene
• Where is The Suspect filmed? Location guide to ITV drama
• Meet the cast of The Suspect

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