ST. LOUIS PARK — Students at a St. Louis Park elementary school gathered around a makeshift memorial filled with stuffed animals and flowers on Friday as they mourned two classmates who died in a landslide during a field trip to a Mississippi River park.

Meanwhile, the city of St. Paul announced it has hired a civil engineering firm to see if it can determine the cause of the landslide that killed 10-year-old Mohamed Fofana and 9-year-old Haysem Sani, and injured two other students.

Minnesota Gov. Mark Dayton attended the tribute to the fourth-grade boys at Peter Hobart Elementary School on Friday, and offered condolences to students, staff and parents.

“I wish I could say something that would make you feel better. I wish I could say something that could explain to you why this terrible thing happened. I can’t,” he said.

“It’s just really sad,” parent Rajni Mishra said. He said his first-grade daughter had a friend on the trip who wasn’t hurt. And while Mishra knows the incident was an accident, he said more should be done to protect students.

“We cannot stop children from going out on field trips,” he said.

The children were exploring a popular fossil area at Lilydale Regional Park when the gravel slide overtook them Wednesday. Authorities say persistent rains saturated the soil and contributed to the slide.

The city announced Friday that Northern Technologies, Inc., will investigate. Parks and Recreation Director Mike Hahm said in a news release that the firm had experience evaluating collapses and natural disasters. It’s expected to have a report for the city in several weeks.

The city has closed off the fossil area until further notice.