A decision by the two big mobile phone companies to stop storing text messages is costing the police an investigatory tool.
Vodafone is no longer storing texts, and Telecom is about to follow suit.
Police were able to obtain copies of text messages, which sometimes gave them valuable information.
The change, caused by the companies' introduction of new equipment, raised debate among police and lawyers about whether a law change should be sought to require the information to be kept.
But police national crime services manager Inspector Bill Peoples said that although the telcos' move would have an effect on investigations, a law change was not practical.
Police can still obtain records of text calls, but not the text.
"It [text content] was a source so we will just have to rely on other means," Mr Peoples said.
Voice calls are not affected by the equipment change.
If police considered an investigation was serious enough, they could apply for an interception warrant which would enable voice and text calls to be captured as they happened.
Text evidence has been important, in particular, in drug investigations where customers have texted orders to "tinnie houses".