Police have begun a search of garages to try to find the body of schoolgirl Danielle Jones, who went missing in 2001.
Assistant Chief Constable Steve Worron, head of Kent and Essex Serious Crime Directorate, described the search of the garages, which are between Goddard Road and Crammavill Street in Stifford Clays in Thurrock, as a "credible line of inquiry".
It comes after police received information earlier this year of "unusual activity" at the site, he said.
The area was not searched during the 2001 investigation and detectives want to know why this did not happen, said Mr Worron.
Danielle was last seen on June 18 2001 at about 8am as she left her home in East Tilbury to catch the bus to school.
Her uncle Stuart Campbell was convicted of murder in December 2002, but her body has never been found.
The schoolgirl's disappearance and murder sparked one of the biggest cases that Essex Police have dealt with, involving more than 750 officers and staff.
Mr Worron said: "We received information earlier this year that there had been unusual activity in the garage block and I am absolutely committed to conducting a thorough and professional search to see if we can bring the Jones family any closer to knowing what happened to Danielle 16 years ago."
Danielle's parents Linda and Tony said in a statement: "We think of Danielle every day and we hope that this latest search may bring us answers about what happened to her 16 years ago."
Campbell has not told police or Danielle's family where the body is and has not shown any remorse, Mr Worron said.