For the first months after the murders they virtually lived with Josie and her father, Dr Shaun Russell, in their home at Granary Cottage, Chillenden. Both say they have become emotionally attached to Josie and her father, a bond which will probably never be severed.
Det Con Tingley, 44, who has three children of his own and a fourth on its way, due next year, said: "She is tenacious. She has got real spirit and that is why she survived."
PC Smith, 51, who has two grown up sons, including one who has joined the police force, added: "Shaun says she is like her mother. If Josie wants to do something, she will make herself do it. At times it has been very, very hard, but she is a very tough little girl."
But as Josie came out of intensive care, and it was clear she was going to survive the attack, it became obvious that the mental scars would be as bad, if not worse, than the physical ones.
PC Smith said: "For a time after the incident, she was terrified of going anywhere. She wouldn't even go out of her hospital room.
"We started by taking her round the hospital grounds, and then to the park, then to places like London Zoo or the Tower of London.
"She was very nervous and clingy and would just hide behind us. She was frightened if she saw cars or men coming towards her - she was obviously deeply traumatised."
But slowly, Josie improved enough to go home, and gradually she helped the officers piece together the events leading up to the murders.
PC Smith said: "One of the things that both of us found was that, when we were talking to Josie, as you can imagine, going through real trauma, it was really useful for her to be given a way of telling people about what had happened to her.
"She was really relieved that she could tell us, and there were moments of real joy when she could tell us."
The two officers spent 14 months holding regular interviews with Josie. Det Con Tingley said: "It got to a point when Josie would roll her eyes when she saw us arriving as if to say `Oh no, not you two again'."
Detective Chief Inspector Dave Stevens praised the officers for their work supporting Shaun Russell and Josie while gathering evidence. "It has taken a huge chunk out of their lives," he said.
The officers take evident delight in her progress over the last two years.
PC Smith said: "I love being with her and I do like to spoil her, buying her fancy clothes and taking her out on trips.
"We both have the same shoe size, and one of the things she likes to do when I visit is swap shoes with me.
"She gave me her favourite flowered Doc Marten boots, which really made me emotional. They now have pride of place in my house."