7/7 detective: The security services obstructed the investigation

Early on the morning of Thursday 7 July 2005 Detective Sergeant David Videcette of the Metropolitan Police Anti-Terrorist squad remembers watching the first reports of a power surge on the London Underground scroll across the TV on the wall of his office. Videcette knew something was wrong. Soon the reality became clear: a terror attack on the London transport system with multiple bombs that would kill 52 people and injure 770 others. From a police perspective, Videcette says: "We had no idea it was coming."

Videcette arrived at the scene of the bus bombing in Tavistock Square at lunchtime and worked through the night. It was only the next day, when he visited a witness who had been standing behind the bus in Tavistock Square, that the appalling nature of the attack hit Videcette. The witness said: "There was a big white flash of light in front of me, and all of a sudden I was covered in blood." When he retrieved the man's clothes "it was like somebody had poured a bucket of blood over him".

It struck Videcette then that 52 families had been devastated by losing the people they loved, and he says he felt a strong calling to do his best to bring those families justice through the investigation. "For the first time I remember feeling the emotional upset."

ID evidence and CCTV footage quickly established the identity of the bombers as Germaine Lindsay, Mohammad Sidique Khan, Shehzad Tanweer and Hasib Hussain – and Videcette began working on the Leeds arm of the investigation, sometimes only returning home to see his family once a fortnight. He became increasingly frustrated that the investigation was only pursuing leads that the bombers had wanted them to find.

The usual interviews with friends and families were often fruitless. "They had, for some months, disconnected themselves so it was like, 'Well yeah, we used to see each other but he'd become very distant over the last few months and I haven't really seen him'."

Videcette says the investigation spent months tracking down who had bought a loaf of bread recovered from one of the bomb factories. "You can imagine doing that 3,000 times with different pieces of evidence, the immense amount of work that we had to do just to find out that actually that was a complete waste of time?"

The key to a breakthrough lay instead in working with the mobile phone data, Videcette believed. "I felt there were lots of things that we could have done differently and I started to look at the phone data."

Using phone data, Videcette put together a comprehensive look back in time to see what the bombers had been doing and who they communicated with. That work, however, brought him into conflict with managers and other members of the squad. "There were internal arguments and fights and conflicts." In particular Videcette believes the investigation was hampered by the relationship between the police and the security services. "I felt we weren't able to progress the things that we should have progressed."

Comparing terrorism to a tree, Videcette says he wanted to cut all the big trees down, while the security services had a strategy that involved lopping off lots of small individual leaves. "It's in their interest to ensure that they are constantly tapped into the trunks of the tree so they know where the branches are and when the leaves are going to come out. Then they can keep saying, 'Well we foiled another attack, we've stopped another leaf on the tree'. I wanted to deal with the trees but I couldn't."

In 2013 Videcette left the police force. Now he has written a fictionalised account of the investigation, to be published this autumn. He plans to donate some of the proceeds to a scheme that helps police officers dealing with post-traumatic stress.