Samarco Mineração SA, the Brazilian firm responsible for the deadly 2015 dam burst in the country, was informed about structural problems to the dam a year before the tragedy, an engineer told the Wall Street Journal. The death toll in the incident rose to 17 and two people remained missing, according to Australia's BHP Billiton Ltd., the co-owner of Samarco.

According to engineer Joaquim Pimenta de Ávila, who worked on the dam, he was consulting for Samarco and found a crack in the company’s Fundão waste-storage facility in September 2014, the Journal reported Sunday. Pimenta de Ávila told the newspaper that he believed the crack showed beginning of a break, and that he alerted Samarco to increase monitoring and reinforce the dam with a buttress.

Nearly 14 months later, the dam broke sending thick red mud rolling down the southeastern Minas Gerais state and trapping lorries, cars and houses in mining waste. The burst also caused significant damage to environment, and is considered as Brazil’s worst environmental disaster till date.

Pimenta de Ávila, a key witness in a criminal investigation of Samarco, told the Journal that he suggested Samarco to construct the buttress at the base of the dam and design it in such a way it could strengthen the dam even in this worst-case scenario. The cause of the burst remains unknown.

However, Samarco lawyer Maurício Campos Júnior told the Journal that it did not get any warning of an “imminent” break from any of its consultants.

“Cracks or surges can occur in any dam,” Samarco said. “The operator’s duty is to report them, evaluate them and treat them adequately, with reports, technical recommendations and contracted projects, as Samarco always did.”

Campos said that Samarco was in the process of strengthening the dam at the time it burst in November 2015. Pimenta de Ávila consulted Samarco to design and supervise the construction of the Fundão tailings dam between 2008 and 2012. The company turned down his bid to renew his contract after it expired in 2012, the Journal reported.

“What I think was lacking was a belief in the worst-case scenario, that the worst-case scenario was viable,” Pimenta de Ávila told the Journal, adding that he also sought clarifications on the buttress design in 2014 but never heard back. He also said that he was not responsible for the dam after 2012.

But, according to Samarco, Pimenta de Ávila was aware of what was followed up to his recommendations and did not protest. “I think this is the conduct of someone who wants to avoid blame,” Campos said of Pimenta de Ávila, according to the Journal.

Pimenta de Ávila’s account comes days after Brazil’s Federal Police accused BHP and Vale SA, the co-owner of Samarco, of environmental crime in the incident. Seven company executives and engineers were also indicted along with consulting company Vogbr, which sends technical reports on the stability of the dam to Samarco, Bloomberg reported last Thursday.

Samarco’s CEO Ricardo Vescovi was among the indicted, the report added citing a police statement.