There has been rising anger in Mexico over the collapse of a metro overpass in Mexico City.
The elevated track on Line 12 fell on to a road, killing at least 24 people on Monday. Many more were injured.
President Andrés Manuel López Obrador said "nothing would be hidden" while the mayor said an external company would be involved in the inquiry.
But family members have been getting increasingly frustrated waiting for information on relatives.
People have held protests calling for culpability as the country comes to terms with the deadliest incident in decades for the city's metro system.
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