Bethan’s jaw dropped and she blinked three times, very quickly.

‘Because either Karen Foster is lying to us, or you’re lying to us. One of you is not telling the truth. Now, Beth Ann, this is your last chance to save your arse. Do you understand me?’

She nodded rapidly, making it abundantly clear that she’d grasped precisely what he meant only too well.

Shep leaned forward, switched on the tape recorder, told it the time and attendees. He then asked Bethan to tell us everything she did and saw from lunchtime onwards on Monday 1st July, 1991.

She sounded desperate, hunted: ‘I was with my mother that afternoon and got back to the Pines at about five past six. I saw Laura Foster waiting for me on the balcony of my room which is on the first floor. Karen had a key to my room and they sometimes watched TV when I wasn’t there. When I got to the door to the building on the ground floor, Laura opened it for me. We walked upstairs together. Laura said she and Karen had been in my room since five p.m. and that Karen had left at six to do the flowers with Peter.’

‘What was Laura Foster wearing?’

‘Jeans and a black t-shirt.’

‘Just remind me briefly of the times again.’

‘I went to my mum’s in Tooting at about two, stayed until five thirty and got back to the Pines at about five past six. I didn’t see Karen until later.’

‘Okay, stick to 6.05; when you got back, how did her sister, Laura Foster seem?’

‘Well … She didn’t seem to be her usual self. She was fidgety and kept pacing around the room, whereas normally she just sat down and chatted.’

‘Did she say anything that struck you as odd?’

‘Not that I remember,’ said Bethan.

‘Did you see Karen again that evening?’

‘Karen came to the room at about eight. She said she couldn’t stay long as she had to drive Peter home. She had a cigarette and some water and then left.’

‘I didn’t know she smoked,’ said Shep.

‘She doesn’t, usually.’

‘Did she say anything unusual?’

‘She mentioned in passing that her and Laura had been in my room earlier, from about five to six.’

‘What was Karen wearing?’

‘Jeans and a red t-shirt.’

‘Did she use your bathroom?’

‘No.’

‘Did she mention anything about an upset stomach?’

‘No.’

‘So she left and Laura stayed. What next?’

‘At about nine, the phone in my room rang. Karen asked for Laura. She took the receiver from me, went white and said something like: “Marion’s been killed” or “Marion’s dead”. She seemed very shaken.

‘During their conversation, Laura started crying. She put the phone down and said Marion had been stabbed and that Karen and Peter had found her body.’

‘You say she was crying, can you describe how?’

‘She was hysterical. She was in a really bad way, even though she didn’t really know Marion. I phoned a cab, gave her ten pounds and sent her home.’

‘Did Karen or Laura have any items with them?’

‘I noticed after Laura had gone home that she’d left a black gym bag under a seat in my room.’

‘Did you look inside?’

‘I had a quick look inside and saw a red t-shirt and a make-up bag on top, but I didn’t go through the rest of it.’

‘Oh come on, what was in the bag?’

‘I told you, I felt bad prying into her personal stuff. I just glanced in the top, saw the red t-shirt and a make-up bag, then closed it again.’

Shep sighed, letting Bethan know that she hadn’t earned her freedom yet.

‘Next morning, when did you next see or hear from Karen or Laura Foster?’

‘I went into work at about eight a.m. I told my boss that Marion had been murdered and that Karen and Peter had found the body. Later that morning, at about ten a.m., I got a call from Karen. She sounded annoyed. She said to me “Bethan, who have you told?” It turned out that Karen had been speaking to one of the hospital bosses and had been surprised to discover he already knew about the murder.

‘Around midday, the porter rang me to say Karen was at the home and wanted to pick up something from my room. I went down to meet her in the foyer. Laura was there too. They said they wanted to pick up the gym bag they’d left behind.

‘We all walked up to my room. Karen looked upset and tired. She said to me again: “We were here just after five yesterday.” They picked up the bag and left.’

Like Peter a day earlier, the more Bethan spoke the more she came to realise that Karen Foster could have murdered Marion, and that her sister Laura may have been somehow complicit in the crime.

‘Had you any dealings with either sister over the next few days?’

‘Laura rang me a few days later to tell me that the police would be calling to see me. She wanted me to call her as soon as they’d been.’

‘Didn’t that strike you as suspicious?’

‘I just thought she was being supportive, as a friend.’

Shep took another loud, deep, disappointed breath.

‘Go on,’ he said, a headmaster tolerating a tall tale.

‘The Sunday after Marion’s murder, the police came to my room at the clinic. DC Young told me that they required a statement from me but, in the meantime could I write down everything I’d done on the day of the murder. I was also asked to recall how long Karen and Laura had been with me and at what times. I was frightened. I didn’t know what to say. If Karen and Laura said they were in my room from five p.m., why should I doubt them? After they left, I phoned Laura and told her about it.’

‘Did you express your reservations to Laura about lying to the police?’ said Shep.

‘I didn’t lie. I believed them. She could tell I was worried but she kept assuring me: “We really were at your room just after five. We were not lying. Just tell the police you were with us at that time.” Why would I doubt the word of a close friend?’

‘Did you not start to wonder why Karen and Laura were so anxious for you to give them this alibi?’

‘I don’t think they had anything to do with Marion’s death.’

‘Marion’s murder,’ Shep corrected her, ‘she was stabbed to death, remember?’

She nodded quickly, obediently, close to breaking.

‘When did you next speak to either Karen or Laura?’

‘I called Karen after I’d made my written statement, to tell her what I’d said.’

‘And how did she react?’

‘She just said “okay”.’

‘Did you speak to her again?’

‘She phoned me a couple of days later and asked me if anyone else at the Pines had been interviewed. She told me again that she and Laura had been in my room from five.’

‘What did you think of this behaviour? Surely you must have wondered why she was so insistent that you stick to your story?’

‘I was beginning to think maybe something wasn’t right.’

‘Oh come on, Bethan,’ shouted Shep, his gag of mispronouncing her name lost in rage, ‘enough is enough. You knew Karen murdered Marion. You agreed to provide her with an alibi. You’re an accessory to the murder of Marion Ryan.’

‘No! I never for one minute thought that. Never. Everyone knows it must have been a man. I think you’re fitting them up.’

‘Are you scared of her, Bethan?’ sneered Shep. ‘Were you frightened of what she’d do to you if you told the truth? Were you frightened you’d end up stabbed to death, like Marion?’

‘No, no,’ she cried, her face screwing up into a hideous ball, ‘I want a solicitor.’

‘You’ll need a solicitor,’ said Shep, ‘because I’ve got a good mind to charge you. Interview terminated at sixteen thirty-two.’

Shep bolted upright, knocking his chair back with an almighty crack. ‘May God forgive you,’ he spat at her bowed, shaking head: her crucifix rattling the table top.

I followed Shep outside and back along the corridor: ‘My God, Lynch, Karen Foster did it. It’s the only explanation. Jesus Christ, they plotted it down to the last detail. That gym bag they left in Bethan’s room held the murder weapon and Karen’s change of clothes. That was a smart move, leaving it there. Even if we suspected them at the very start, we never would have searched Bethan’s room. What Bethan saw in that bag had to be the red t-shirt Karen wore when she helped carry out the murder. Of course it’s all probably in the bottom of the Thames now.’