As the missing York chef's family and friends reached a five year milestone since her disappearance, Peter Lawrence made another heartfelt plea for information.
Ms Lawrence, then 35, was last seen after leaving work at Goodricke College, part of York University, on the afternoon of March 18, 2009. After speaking to both parents separately on the telephone that night, she has not been seen or heard from.
Yesterday (Monday, March 17) Mr Lawrence gave a press conference in York, where he made another appeal to anyone with that key piece of information to get in touch and end his family's torture.
"No-one knows unless they are in the same position as we are what it means every day and most nights wondering, worrying.
"Claudia are you safe, is someone holding you, have you been hurt and even, of course, are you alive?" he said.
"It's now five years on and it is more than 18,000 of those days and nights.
"It's an awful long time for anyone to be in this position. It eats into you. It's like a cancer. It just gets worse and worse. There's no resolution until we know what happened to Claudia."
He said he is convinced someone does know what happened to her, or has some information about her disappearance.
"If you were that person and you are watching, listening or reading this, please, please do realise what it is doing to us. It just eats into you like a hole and it is a torture."
The disappearance of Ms Lawrence, whose parents lived in Darlington before moving to Malton, where she was raised, has become one of Britain's most high profile unsolved cases.
Police believe she was murdered, and finding out what happened to her became one of the first tasks of North Yorkshire's major crime unit when it was relaunched towards the end of last year.
Significant information thrown up by that review is to be aired on the BBC's Crimewatch on Wednesday (March 19).
Mr Lawrence said North Yorkshire Police Chief Constable Dave Jones had made a personal commitment to find out what happened to his daughter shortly after he took over North Yorkshire Police.
"That was something that he really wanted personally as well as professionally," said Mr Lawrence. "He gave that pledge and this is the heart of it.
"I knew they would find something new.
"What that information is remains to be seen. But if you get a new experienced team looking at something they're going to find something new."
The Crimewatch appeal will be aired on BBC 1 at 9pm on Wednesday.