(CNN) No trace of explosives has been found at the site of the helicopter crash that killed the new governor of the Mexican state of Puebla and her politician husband, a government official said Tuesday.

Puebla governor Martha Erika Alonso and her husband, Senator Rafael Moreno Valle, died in the Christmas Eve crash in central Mexico, as did the pilot, co-pilot and a fifth person on board, according to officials.

"After an exhaustive and detailed analysis of the remains of the aircraft, we found no explosives or foreign substances that could have caused the aircraft to crash," Public Security and Civil Protection Secretary Alfonso Durazo said at a Mexico City news conference.

Durazo said investigators used bomb-sniffing dogs and other specialized equipment at the crash site Tuesday in an effort to detect traces of explosives.

Authorities believe the helicopter crashed nose first.

Read More