Last Boxing Day, I woke up feeling slightly sluggish due to the excesses of the previous day. So I headed out for a ramble in the forest with my wife, Michelle, our two kids and one of their friends.

We were deep in the woods, playing hide and seek, when I was confronted by the most incomprehensible sight: a man in his 40s hanging from a tree.

As I moved closer, I saw that he was alive, just, and was clinging on to the underside of the branch. It was as if he was in two minds about letting go. His face was a nasty shade of purple, he had a foam pouring from his mouth and he was making a horrific noise – a sort of sobbing wail. He can't have been there long.

I tried to release the tension of the ligature by putting one arm around his feet while using the other to push up under his bottom. I work in forensics and visit crime scenes all the time, so I wasn't upset or freaking out. In fact, I remembered how important it is in situations such as this to keep people calm, so I started talking to him in a friendly, conversational way. I said, "Hello, mate, let's get you down."

As I was standing there supporting the man's weight, a phone rang in his pocket – it was a jingly Christmassy ringtone, which seemed bizarre, given the circumstances. I realised later that it was probably the police, who'd already been alerted by the man's family, because he'd told them he was going to end his life. They would have been calling to try and get him on the line for long enough to track his location.

At this point, Michelle and the kids appeared, shouting, "Found you!"

The children asked what I was doing, so I said I was just trying to help this poor man who had got stuck in a tree and couldn't get down. They were curious, but I wanted to get them away because it could have been quite frightening, so I shouted at Michelle to carry on playing while I scanned the woods for anyone else who might be able to help.

I didn't have a penknife to cut the man down, so I fished out my phone to call 999 while trying to support him. Meanwhile, I was shouting, "Help, is anyone there? Has anyone got a knife?" I was still holding the man up when the first policeman arrived. More police, two fire engines, an ambulance and a helicopter followed. That seemed a bit much: it could have scared him.

It hasn't upset me – in forensics, we're too thick-skinned for that – but it upset Michelle; luckily, the children were too young to understand what was going on. Even so, in my line of work we don't see too many bodies: we're the ones called to a scene after the police and paramedics have been there. Our job is to make sure there's been no foul play, and to look for evidence, sources of DNA. We often get told off for laughing and joking, told that we're being inappropriate. But it's gallows humour – "Look, lads, here's a bit of finger," that sort of thing. It keeps you sane.

I suppose the man was lucky it was me who found him, rather than someone less experienced, who might have been frightened and unable to think clearly. But all I did was call for help and then try to preserve his life – hopefully anyone would have done the same.

The kids were back by now, so I handed over to the police, keen to get them home. We still go back to the woods to play hide and seek, but Michelle steers us away from that particular spot. My four-year-old son refers fondly to "the silly man stuck up a tree".

Apparently, the man survived. I wonder if he had an instinct just to hold on. I must have been thinking about him after it happened, because when I went back to work after Christmas, I checked on his police report. It hadn't been updated, which meant he was still OK. It was good to find out.

If it had been my other half who found him, Michelle would probably have been in a blind panic, so I'm glad it was me. And I'm glad that I was able to help someone who was in a bad place.

• As told to Hannah Booth.

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