‘An exit bag, also known as a suicide bag, usually consists of a large plastic bag with a draw cord – which can be something as simple as an elastic band slipped over the head or a piece of string – to close the bag. A pipe is inserted into the bag and sealed in place using something like parcel tape. This pipe is connected to a cylinder containing helium or nitrogen, both of which are readily available – particularly helium – and the gas is fed into the bag. For the victim, it’s a painless death. They breathe normally and comfortably and are unconscious through lack of oxygen in a few seconds. Death takes a little longer – maybe ten minutes – but the victim feels nothing.’

There was a buzz in the room, and Becky nodded to Lynsey. She had done well, and had it not been for the telltale flush that seemed to plague her, Becky would have thought she had all the confidence in the world.

‘Thanks, Lynsey,’ Tom said. ‘That’s a perfect description of what has become something of a favoured suicide method. As you probably know, helium can be bought from shops that sell balloons for parties. If nitrogen was used though, it will be difficult to prove. There will be no trace of it in the body because the air we breathe is over seventy per cent nitrogen. Either way, we think the circular marking on the floor might indicate where the cylinder was placed.’

Becky looked around at the team. People weren’t slouching now. They were turning to each other and talking in low voices. This was new. They hadn’t had a case like this before, and Tom’s eyes briefly met Becky’s again.

‘There was no cylinder at the scene, no plastic bag, and nothing but a tiny scrap of parcel tape. So if this really is how she died, she had help. Someone went with her to that place, and whether she willingly submitted to having the bag placed over her head or was incapacitated before she died, at best this is a case of assisted suicide, which is a crime. Alternatively, this has all the hallmarks of a very clever murder.’

CHAPTER 10

10

Time is passing too quickly on this holiday. I feel as if I’m racing towards the moment when I will have to return home and face reality, and I can’t bear the thought. I struggle to focus on conversations and find myself tuning out whenever I’m in a group, letting others speak.

It is as if Thea has read my mind and come to my rescue, because earlier she took me to one side. ‘We’re going to get a separate table for dinner tonight,’ she said. ‘Would you like to join us?’