Turning the blade over in his hands, Finn’s face was a tangle of emotions. As tears slid down his cheeks, he continued to stare at the blade.

Kate remained frozen to the spot. Her mind had been connecting dots without realising what the final picture was supposed to be. In every subsequent conversation Finn had spoken of his love for Amy and how he felt guilty about failing to protect her. How had she fallen for his lies?

He’d made no movement towards her, but the threat of the weapon in his hands quelled Kate’s urge to rush at him.

She jumped as he finally spoke. ‘I didn’t mean for it to happen.’ His words were barely discernible beneath the weight of anguish. ‘I didn’t know what else to do.’

Kate’s breathing had quickened, but the rise and fall of her chest was steady. Trying not to draw attention to any sudden movement, her fingers slowly reached into her trouser pocket and slid her phone out and onto the sofa. Delicately brushing her finger over the print sensor, she unlocked the screen and tried to call the first name in her contacts without looking.

‘Tell me what happened? I’m sure—’

His head snapped up. ‘Shut up!’ His eyes were still filled with tears, but there was confusion in the darting movements of the pupils. ‘I killed her… I killed Amy…’ His shoulders seemed to relax as the pressure of the burden he’d been carrying for the past year lifted.

‘Finn? Look at me,’ she said, fixing him with a stare, the phone hidden by her hand. ‘It’s okay. I’m your friend, remember? Just tell me what happened.’

He thrust the blade forwards defensively, but there was still a six-foot space between them. The light overhead glistened off the blade. ‘You won’t understand. It wasn’t my fault… not really. It was an accident… she… Oh God, what have I done?’

Kate gently flapped her free hand in an effort to calm him. ‘Please, Finn, sit down and tell me what happened. If it was an accident, then I’m sure we can—’

His eyes darted left and right, but his knife arm remained flexed, ready to strike if threatened.

‘Amy called me from the theatre,’ he began, his eyes fixed on the wall as the memory played out in his mind. ‘She said she’d had a tough week and was looking forward to the family catch-up at the weekend. She asked if I’d pick her up and drive her to my dad’s that night. I didn’t feel great, but I’d have done anything for her. She knew that. I loved her. She was more than my sister. I collected her from a car park near the Southbank. She said she needed to pick up a few bits and pieces from home, so I drove us to her flat. She told me to come up while she packed. She opened some wine and…’

Kate couldn’t tell how much of the conversation her phone was capturing. She needed to get him closer to the microphone.

‘I could see her changing from the mirror in her bedroom. She never realised just how beautiful she was. I don’t know if it was the wine, but I couldn’t stop watching her. She caught me looking and asked me to come into her room and adjust the straps on her top. My fingers trembled as they brushed the skin of her back, and I leaned down and kissed the nape of her neck. Her hand brushed my cheek, and she turned and we couldn’t keep our hands off each other. She pulled my shirt off and undid my trousers, but suddenly freaked out.

‘She wanted me, I’m certain of it, but as I tried to kiss her again, she pushed me away. I knew she was scared of what it could do to our family, but I’d never wanted her so much. It’s not like we were related by blood.

‘I told her to calm down, but she started calling me names. She was trying to make me angry, but I could never be angry with her. She stormed out of the bedroom, but tripped on something and caught the back of her head on the corner of the coffee table. There was no blood, no sound. She just lay there, her eyes closed.’

Kate pictured the post-mortem photographs. ‘You tried to rape her, Finn.’

‘No! She wanted me, but then she freaked out.’

‘The pathologist found bruising around her thighs.’

‘It wasn’t like that. She wanted me to…’

She could see in his face that he’d been telling himself the same lie for so long that he was now almost convinced it was true.

His head dropped once more. ‘I thought she was play-acting at first. But as I felt for a pulse, I couldn’t find one. I didn’t mean to kill her, but I was the only one there and I knew nobody would believe my story. I panicked. I couldn’t face jail for something I hadn’t done. And then I spotted the knife in a box near the computer. There was a packet of cleansing wipes too, and photographs of the other crime scenes. Suddenly the answer was so clear. She’d left me the tools to save myself.

‘I carried her down to the alley and removed her underwear. She’d told me how the killer wiped his victims down, and slashed them with the knife. I knew that if I could make it look like he’d done it, then nobody would suspect me. It was so difficult to cut her up like that. I had to finish the bottle of wine to get the courage to do it.’

Finn looked back up at her. ‘I was ill for days. I was convinced you lot would see through what I’d done and come and arrest me, but you seemed so keen to go along with her being another of the serial killer’s victims that I thought it would be okay. I made a promise that I would do whatever it took to find the monster she’d been hunting and ensure he paid for all the pain he’d caused. And now, now we have!’

Trying to keep him calm, Kate raised the phone. ‘I can call one of my colleagues to come and take a formal statement from you. I will explain the situation and—’

He dived forward, striking her hand with his own, sending the phone crashing across the room and into the wall. ‘I can’t go to prison for what happened. It wasn’t my fault.’

Kate’s eyes widened, the blade only inches from her face. ‘You don’t want to make things worse, Finn. Let me take you in. It’s what Amy would have wanted—’

His face flashed with anger. ‘How would you know what she wanted? You’re just as responsible for what happened to her. And now – now you’ve left me with no choice…’