Inspector Gareth Thomas from Dyfed-Powys Police is now giving evidence at Mold Crown Court.
He describes how the first night was a "hasty, all-hands-on-deck" response, but it then progressed over later days and weeks to a full systematic search.
With 689 separate search areas, it became the biggest search in British police history, he says.
The fire service, RNLI, coastguard, dog handlers and professional volunteers were all involved in a six-month operation, from October through to April.
The River Dyfi was searched on three different occasions by three different teams, and sonar technology used.
Asked by prosecutor Elwen Evans QC about his confidence in the search operation, Inspector Thomas replied "I'm extremely confident if he had put her in any of those areas we would have found her."