(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.
"The helicopter's tailwheel was found elevated and the rudder is below it, which leads us to believe that it crashed at a 60-degree angle," Deputy Transportation and Communications Secretary Carlos Alfonso Moran told reporters.
Moran said the cause of the crash is still under investigation, with the assistance of Canadian aviation experts. The US National Transportation Safety Board will not be able to assist because of the government shutdown, he said.
President Andrés Manuel López Obrador offered his condolences to the victims' families shortly after the crash and vowed a transparent investigation into its cause.
The crash occurred at 2:40 p.m. local time Monday, about ten minutes after takeoff, Durazo said Monday night. Communication with the aircraft was lost and a crash was then heard, he said.
"When the aircraft was in flight some three nautical miles from the Puebla airport, it suffered an apparent failure which hasn't been determined yet," Durazo said.
The helicopter pilot and co-pilot were identified as Captain Roberto Cope Obregon and Captain Marco Antonio Cabera Romero, Durazo said. Durazo said the fifth passenger still has not been identified.
Durazo said the aircraft was found in the town of Santa Maria Coronango. The helicopter was an AgustaWestland AW109, which was owned by the Puebla-based company Servicios Aereos del Altiplano, Durazo said.
Alonso and Moreno were headed to Mexico City, Mexico's Communications and Transportation Secretary Javier Jiménez Espriú said Monday.
Espriú said both the aircraft and pilots had all the necessary authorizations and paperwork.
Alonso had assumed the governorship of the east-central Mexican state on December 14 after narrowly defeating her opponent. She was the state's first female governor.
Moreno was a senator, and governor of Puebla from 2011 to 2017.
Marko Cortés, head of the center-right National Action Party, said via Twitter Monday that he was deeply saddened to hear about the accident.
"We are in mourning," he wrote.
On Twitter Sunday evening, Alonso offered good wishes for the holidays to the families of Puebla and said the coming year could be peaceful and prosperous despite the great challenges facing the state.
López Obrador said via Twitter that his government investigation of the crash will "tell the truth about what happened and act accordingly."