A "sniffer tube" could replace dogs in the arsenal of tools to locate hidden graves, say researchers.

A new technique uses a long tube to quickly sample the air above suspected gravesites.

The specially coated tube can spot tiny amounts of a chemical linked to the breakdown of animal remains, up to months after the remains are buried.

The research is published in Forensic Science International and highlighted in New Scientist magazine.

The task is to outperform the premier detector of hidden explosives, drugs, or humans alive or dead: the sniffer dog. But as much as dogs can be trained, it remains unclear what exactly they perceive.

"We're not really sure what the dogs are sniffing or what they're focusing on," said Tom Bruno of the National Institute of Standards and Technology (Nist) in the US.

"And dogs can be difficult to control, and uncertain," he told BBC News. "Recently we've come to think dogs aren't sniffing an explosive, but cyclohexanone, a chemical used to re-crystallise the explosive.