Before a tragic landslide killed two young students on a field trip to Lilydale Regional Park this past spring, slope failures, rockfalls and other changes had occurred within the park and elsewhere along the Mississippi River bluffs.

But two independent investigations commissioned by the city of St. Paul concluded that despite evidence of soil erosion, the city couldn't have predicted or prevented the fatal landslide.

St. Paul Mayor Chris Coleman announced the results at a Thursday news conference accompanied by investigators who led the inquiries.

"The tragic nature and consequences of what happened were not predictable or forecastable and at the end of the day, the city staff had acted appropriately in response to what they knew about the general conditions in Lilydale Park," Coleman said.

Fourth-graders Mohamed Fofana, 10, and Haysem Sani, 9, from Peter Hobart Elementary School in St. Louis Park, died after a cliff at the park collapsed on May 22. Two other children were injured. The students had been hunting for fossils at the popular site, when the waterlogged hillside gave way.

Following the incident, the city of St. Paul hired Hamline University School of Law Dean and former Assistant U.S. Attorney Don Lewis to lead a review of internal processes and communications leading up to the landslide. Northern Technologies Inc. (NTI), a civil engineering firm, was tasked with examining the collapse's cause.

Lewis' team concluded that the city did know that soil erosion was an environmental threat within Lilydale park, however, the city didn't know that soil erosion was a threat to the safety of visitors to the fossil ground site.

A 2009 study noted there was "erosion along the walls of the former clay pits" and recommended that the city survey erosion and identify stabilization measures, but the city hadn't done so by the time the landslide occurred.

In May 2011, a "slope failure" or landslide occurred near a waterfall within the fossil ground site just north of the east clay pit, but nobody witnessed it. In February of 2012, forestry supervisor Scott Kruse also observed soil erosion while ice climbing in the clay pits and notified the parks and recreation operations manager that "the whole hillside is at high risk to slide in heavy rains." However, the study said Kruse's e-mail was interpreted as concerns about the environmental impact of the soil erosion.

"What may seem clear now in retrospect was not so clear before the May 22nd incident," Lewis said. "Our investigation suggested that city employees may not have fully appreciated or understood the meaning of what they were observing in the park."

Attorney John Goetz, who is representing for the families of Mohamed Fofana, Haysem Sani and one of the other boys who was injured, had several issues with the reports. Goetz said the 2011 landslide that happened about 50 yards from where the fatal landslide occurred during similar rainy conditions was an indicator of future problems. "To say [city staff] didn't know of the risk was pretty incredible," he said.

Goetz also wasn't convinced that the fatal landslide was just caused by nature. He pointed out that there was a culvert that fed water into the area where the landslide occurred. Previous clay mining could have also made the area unstable, he said. Goetz said claims are being considered against both the school district and the city.

Mohamed Bah, one of Mohamed Fofana's uncles and president of the Guinea Association/Community of Minnesota, said the results of the investigations, which he said the family wasn't informed about, didn't make sense.

"If they had knowledge about the area that it was risky, why would they send vulnerable kids there?" Bah asked, citing the 2011 slope failure.

Bah said parents wouldn't have sent their children on the field trip if they had known that it was dangerous. He said his family is still mourning the loss of his nephew.

"Somebody must be held responsible for this," he said.

Reached at work early Thursday night, Haysem's mother Sartu Nagayo said she hadn't heard what the investigations had concluded so she couldn't comment on them. "The only thing that I know is that I sent my son to school and then [later] I found out that he was dead."

The investigation led by Northern Technologies Inc. Senior Engineer Ryan Benson, said "additional groundwater accumulation" from recent rains was a factor in the landslide. The opinion went on to say that it doubts any recent "man-made" activities in the area played a role in the landslide.

"There was no way to predict with any high level of accuracy exactly where in the park, the magnitude of the slide or the exact timing of that slide," Benson said.

Another landslide is likely to occur in the future, he said. In addition, even if the city had conducted the erosion evaluation survey recommended by the 2009 study, it probably would have had little impact on whether the fatal landslide could have been foreseen, he said.

Jon Kerr, head of the Friends of Lilydale Park, said his group wants to see the fossil site, which he called "a really wonderful laboratory" eventually reopen.

"We don't want to civilize that park. We don't want to pave the whole park to make it safe," Kerr said.

But he said there could be other ways to improve safety such as informing people more about the risks.

For the time being, the city will continue to suspend permits to the fossil site as it evaluates the future of the park. With the help of the National Park Service and other partners, the city is working on assessing and reviewing procedures there, Coleman said.

"We are never going to be able to create a perfectly safe environment in Lilydale. It can't happen," he said. "But we do believe that working with our partners … we can learn and implement a protocol that will allow us to once again reopen Lilydale Park."

Staff writers Chao Xiong and Paul Walsh contributed to this report.

Nicole Norfleet • 651-925-5032