I think that the ITV documentary should be viewed alongside the BBC documentary The Murder of Jill Dando available on iPlayer here
www.bbc.co.uk/iplayer/episode/m0003w40/the-murder-of-jill-dando
The BBC documentary spends a lot more time interviewing the investigating police officers and what comes across very clearly to me are officers who are so fond of their hypothesis that they fail to consider it as a provisional hypothesis and fall victim to confirmation bias.
Watching these cops in action reminded me of the excellent series of documentaries, also on BBC, The Yorkshire Ripper Files, 1st episode here on BBC iPlayer
www.bbc.co.uk/iplayer/episode/m0003m05/the-yorkshire-ripper-files-a-very-british-crime-story-series-1-episode-1
I am also reminded of the murder of Rachel Nickel and the subsequent investigative farce including using a female police offer in a honey trap to try to ensure the completely innocent Colin Stagg into confessing.
This documentary is very good
Rachel Nickell The Untold Story
www.dailymotion.com/video/x6gdnub
One problem that is quite obvious in all of these situations is an over dependence on criminal profiling and a dismissal of old-fashioned investigative policing. The narcissism of certain officers involved is also evident.
Another factor, one that affects the narcissism of the officers, is the involvement of the press and media around these cases. Observing any phenomena always influences the phenomena and this is true of police investigations as much as anything else, possibly more so as egos and reputations are on the line.
FWIW I think that criminal profiling is interesting and may at times be useful, just like intuition can sometimes be helpful and useful, but to take a huge investigation along a trajectory founded on intuition and / or psychological profiling is completely insane, and, as happened in the Rachel Nickel murder and with Peter Sutcliffe, can leave dangerous serial killers free to murder more victims.