By Dave Graham and Diego Oré
MEXICO CITY (Reuters) - An auditor's third report on a deadly Mexico City metro accident last year for the first time identified maintenance shortcomings as one of four causes of the collapse of the rail overpass, according to an unpublished version of the study seen by Reuters.
A Mexico City official familiar with the document confirmed the authenticity of the report by Norwegian firm DNV, which was produced at the behest of the city's government to determine the cause of the crash that killed 26 people.
It was meant to be the last of the auditor's three reports since the May 3, 2021, crash on the Line 12 metro service, and it was the first one to cite maintenance as a main cause, according to a Reuters review of the studies published by the city.
Spanish newspaper El Pais published details of the report on Monday. Reuters was unable to establish who leaked the report and for what reason.
The report identifies what it calls four "barriers" which, had they been in place, would have prevented the overpass collapse. Three related to the design, construction and process of supervising the works.
The last point addressed maintenance. In its findings, DNV said it had received "no evidence" that the required inspections on the metro line were performed.
According to the DNV report, the maintenance manual for the Line 12 stipulates that inspections of the structure are carried out quarterly, semi-annually and annually depending on how old the components are.
"The failure to conduct inspections of the viaduct and adhere to the inspection requirements of the maintenance manual is a root cause of the failure," the final report states.
Who exactly is responsible for performing the inspection work was "not clearly specified," it said.
What caused the accident is politically sensitive because the line was built when Foreign Minister Marcelo Ebrard was mayor of the city from 2006 to 2012, and it collapsed 2 1/2 years into the term of the current mayor, Claudia Sheinbaum.
The two are among the top contenders to become Mexico's next president when elections are held in 2024, opinion polls show.
The report has yet to be made public because Sheinbaum's administration - which hired DNV - has rejected the findings, saying they were biased and the methodology flawed.
Sheinbaum, who entered city hall in December 2018, told a news conference on Monday the final DNV report had a "political bias."
To support her claim, she reiterated her assertion that the firm used a lawyer prejudiced against the government to help craft the report, and said that DNV had leaked the findings, breaching a confidentiality agreement.
The city previously identified the lawyer as Hector Salomon Galindo, who held jobs in the previous government. He could not be reached for comment.
Sheinbaum also said on Monday maintenance of the line had not been a problem and that the inspection logs were public.
DNV last week in a statement defended its findings and methodology, and responded to Sheinbaum's assertions about the lawyer by saying the report was produced without the involvement of anyone with a conflict of interest.
DNV did not respond to a request for comment on Monday. It also did not respond to repeated requests for comment on details of the leaked study or why maintenance issues were not flagged in the earlier reports made public by the city.
Sheinbaum, who last week called the report "deficient, poorly executed, with technical problems, tendentious and wrong," said the city was in the process of terminating DNV's contract and filing a lawsuit against the firm, because it had diverged from the methodology agreed in its contract.
Asked for comment about the leaked report's findings ahead of Monday's news conference, the mayor's office said the briefing would set out the city's position.
Ebrard's ministry said it had no comment on the media reports. The office of his successor as mayor, Miguel Mancera, did not immediately reply to a request for comment.
Although the report became public this week, the copy seen by Reuters was dated Oct. 28. Reuters was unable to ascertain whether it was later revised.
(Reporting by Dave Graham, Diego Ore, Cassandra Garrison and Daina Beth Solomon; Editing by Stephen Eisenhammer and Howard Goller)