On June 17 1994, the 28-year-old kissed his wife Christine and his seven-month-old son Luke goodbye to start his early shift, and never returned. He was stabbed to death that afternoon by Philip McFadden, who had stopped taking his schizophrenia medication.
Now just days before the 20th anniversary of his death, Christine has decided to speak out for the first time about how she has moved on with her life.
Christine's world fell apart when her husband of less than two years was killed but she says she went into "remote control" mode because she had a new baby to care for.
It took a long time to come to terms with her loss but now Christine, 54, who has an MBE for her tireless work helping bereaved families of dead police officers after launching her charity Care of Police Survivors (Cops), says: "I have moved on with my life. I still have days that are hard, but in general life is pretty good."
Christine, from Kilmarnock, Ayrshire, has a new partner ,Stuart McAllister, also 54, who is a volunteer for Cops and a trustee for her other charity the Scottish Police Memorial Trust, but they do not live together and have no plans to marry.
Christine said: "We met through our mutual friend Jim McNulty, who was the focus behind the Scottish Police Memorial Trust. We were the three people behind it all and we became close.
"Lewis wouldn't have wanted me to be alone for the rest of my life and would have wanted me to move on."
Stuart worked in Ayrshire and Lewis was Glasgow-based but he remembers the day he found out about the killing very clearly because it was the same day as his son Fraser's birthday.
For the first nine years after her husband's death, Christine buried her grief and devoted her life to bringing up Luke, who is now 20 and studying for a science degree at the University of the West of Scotland.
It was only when she was introduced to other grieving families and went on a trip to the US to see how a support group worked that she realised how much of a need there was back home for similar help and she threw herself into campaigning to help survivors.
Her son Luke has no memory of his father but Christine says he is the spitting image of Lewis.
Christine said: "Lewis will never been gone so long as Luke is here, there is definitely a part of him still living on. Luke is his double.
"It's nearly 20 years on but the pain never goes away, you get used to it. It becomes part of your life. It doesn't hurt in the same way and life gets easier."
She added: "Lewis was so excited about having his first child but he missed all the milestones.
"He didn't see him crawl, he never saw him get his first tooth, walk, speak... he missed everything - his first day at school and sports days. He was looking forward to taking him fishing one day. He was a keen fisherman and that was one of his main plans."
The charity she helped establish has supported more than 300 families all the over the UK and gave support to the families of the two female police officers, Fiona Bone, 32, and Nicola Hughes, 23, who were shot dead while on duty in Manchester less than two years ago.
Christine has organised an event in memory of her late husband, titled Lewis Fulton - A Night To Remember, tomorrow night at the Lochinch Police Club in Pollok Country Park in Glasgow to mark the 20th anniversary of his death.