A book has been launched investigating the disappearance of Yorkshire chef Claudia Lawrence, four years after she went missing.

Lawrence, who was 35 when she was last seen in 2009, was working at the University of York and showed no signs of abnormal behaviour before she disappeared.

Gone: The Disappearance of Claudia Lawrence and Her Father's Desperate Search for the Truth, has been released today (14 March) by Random House.

Author Neil Root looks in depth at the theories surrounding Lawrence's disappearance, drawing on interviews with family and friends.

The last time anyone heard from Lawrence was when she sent a text message to a friend at 8.23pm on 18 March 2009.

Four years on, police still have no leads or evidence as to what happened to her that night, or in the early hours of the following morning.

So far the investigation has cost more than £750,000 and Crimestoppers is offering a £10,000 reward for information leading to the arrest of the person involved in her disappearance.

Police suspect murder

At the end of February, Martin Dales, spokesman for Lawrence's father Peter, said: "Today is the 39th birthday of York chef Claudia Lawrence who has been missing from York since March 2009.

"I cannot believe that we are yet again at another birthday for Claudia and there is still no news as to what has happened to her. All anniversaries are hard for the family and friends to cope with and it is unacceptable that there is still no closure - good or bad.

"Out there are some heartless persons who know something but they don't have the guts to tell the police what they know. How low can people get - it's outrageous and continues, after four years, to cause immense damage to Peter and the family.

"So I make a further appeal to those who know these answers. How can you sleep at night knowing you know the answer? How can you live the lie with yourselves? Have you no feelings for those who are suffering because of your misguided silence?

"Do what you know in your heart of hearts is right and end the misery of all those who love and care for Claudia - even if you don't."