‘Keep it clean and quick. Don’t make any unnecessary conversation with him. Take him down, caution him. I want his flat checked thoroughly and everything seized. All items of clothing. We don’t know what might have a victim’s DNA on it. Also, focus on electronics. We know his primary focus is on screening deaths and that he uploads footage regularly, so phones, computers, laptops, cameras. Keep the use of force to the absolute minimum – no one gets heavy-handed. I won’t have his lawyers challenge us in court over procedure. No one talks to him in the van on the way to the station. The cuffs will be correctly applied and they mustn’t leave marks. Questions?’

‘The Jon Moffat killing suggests he’s familiar with guns. What if he’s armed, ma’am?’

‘You’re all wearing protective vests. If you suspect he’s armed, stay back and let armed units deal with him. The priority then will be to establish that there’s no one else in the flat. All other flats in the block must be secured before we go in.’

Tripp’s phone rang and he walked away from the group.

‘Right, moving in one minute,’ Ava said. ‘Keep in radio contact. Each team has been assigned a floor. Call it in once you have your area safe. No one uses a doorway after that until the safe signal has been given. Let’s go.’

They started jogging towards the allocated building entrances.

‘A couple of people have called the incident room for you, ma’am,’ Tripp said as they got close to the building exterior. ‘Lance Proudfoot, who I think is DI Callanach’s friend.’

‘Okay,’ Ava said as they entered. Callanach was the last distraction she needed right now. ‘And?’

‘Someone from traffic. Not sure what that was about. They left a number and asked you to call back. I’ve forwarded the details to your phone.’

‘Follow me,’ Ava said, taking the first staircase, nodding to other units along the way as they quietly knocked on one door after another, showing their ID badges before giving whispered explanations to each resident about their purpose and what was about to happen. Bolts could be heard slipping into place with each floor they left.

RJ lived on the fourth, and top, floor, at the end of the corridor.

‘Limited neighbours who might hear or suspect something,’ Ava said. ‘Innocuous flat, within easy reach of the Queensferry Crossing. Makes sense that he managed to get to the Stephen Berry incident quickly.’

In front of her was a team of officers ready to use force, if necessary, to enter the apartment. She checked her body armour one last time and gave the go signal.