A man has been arrested on suspicion of the 1994 murder of 13-year-old Lindsay Rimer.
Police said the man was arrested at an undisclosed prison where he is serving a sentence for other offences.
The man, who is being interviewed today and tomorrow, is expected to be bailed and returned to prison while enquires continue.
Officers are also interviewing a number of potential witnesses in the Hebden Bridge and wider Halifax area.
Lindsay left her home to buy a box of corn flakes late during the evening of 7 November, 1994, but didn’t return home.
Her body was then found in a canal close to her home six months later.
Following today’s arrest, senior investigating officer, detective chief inspector James Entwistle, said: “We remain very firmly committed to doing everything we can to get justice for Lindsay, and to give her family the answers they still so desperately need after all these years.
“The arrest we have made today comes as a result of our continued focus on progressing the investigation.
“We are keeping Lindsay’s family updated and, while we appreciate the understandable public interest that today’s arrest will bring, we do not anticipate any immediate developments at this stage.
“Although it is now more than thirty years since Lindsay was murdered, we remain convinced there is someone out there who has vital information that could finally help to ease her family’s pain, and we urge them do the right thing and tell us what they know.”
Anyone with further information has been urged to contact police by calling 101 quoting Operation Posemill, or sending a text or voicemail to 07707147314.
