I headed into the centre of town, following a path that fringed the old shipping canals. In an arcade off the high street, I found a coffee shop, grabbed a table, removed my laptop and put in a search for Isaac Mills. I quickly found him online – but what there was amounted to very little.

He had no social media presence at all – no Facebook, Instagram, Twitter or LinkedIn; not even the shell of a profile that he’d set up but never filled out. There were no photographs of him, certainly nothing as crude as a selfie, and all of that fed into the description of Mills that Ewan Tasker had given me over the phone: when you weren’t much of a socializer, someone who preferred not to go to the sort of get-togethers that led to pictures and postings, social media was never going to be a priority. I was surprised, though, not to find a mention of his name in relation to Seiger and Sten, the law firm he told me he worked for.

Instead, the only results of any significance were three newspaper stories, all different accounts of the same event. I clicked on the first. It was uploaded to the Mail Online in October 2009, and had the headline: OFF-DUTY COP HAILED A HERO FOR STOPPING ARMED ROBBERY ON HIS DAY OFF. Underneath that was a series of pictures, all taken in what appeared to be the same street in Keighley, the town in which Mills lived. He was smiling broadly for the camera as he shook the hand of the store owner whose shop had been targeted.

An off-duty police officer was hailed a hero on Tuesday after disarming a gunman who held up a convenience store in West Yorkshire.

Detective Sergeant Isaac Mills, 42, was out walking his dog when he decided to stop for milk at a corner shop run by Mirat Pridesh, 66, in his hometown of Keighley. What Mills didn’t know was that, inside the shop, 22-year-old Anthony Snead had a pistol pointed at Mr Pridesh’s head.

‘I didn’t realize what was going on to start with,’ Mills admitted. ‘The first thing I remember seeing was Mirat emptying out the till, which I thought was odd, and then I came further in and looked around the end of one of the shelves, and I could see a young lad in a hoodie pointing a gun at him.’

Because Snead was wearing a hooded top, he failed to see Mills enter the store – a stroke of luck that Mills used to his advantage: ‘I looped around one of the rows of shelves and came up behind him. I don’t mind admitting my heart was beating fast, but I managed to grab the gun, get it out of his hand and get the kid on to the floor.’