MEXICO CITY  They were 20 men, kidnapped in broad daylight soon after they arrived at the Pacific resort city of Acapulco for what their families said was a guys’ vacation.

That was five weeks ago, and their fate has been a mystery since then.

But the discovery of a mass grave in a coconut grove on the city’s rural outskirts, after an anonymous tip, may provide the answer many people feared.

The authorities on Wednesday recovered 18 bodies from the grave, and family members of the missing men were traveling to Acapulco, where they will be asked if they can identify them.

A call on Tuesday led the authorities to the coconut grove, where the bodies of two men lay with a note saying they had killed innocent people. It was signed by CIDA, or the Independent Cartel of Acapulco.