The civil engineer hired by the city of Surfside, Florida to investigate the site of the collapse of the 12-story condominium tower Champlain Towers South said Tuesday there could be several factors behind the tragedy.

“I feel very comfortable that we will be able to find out, maybe not a single cause, but two or three things that contributed and / or caused this failure,” said Allyn Kilsheimer, who has other disasters like that Oklahoma City Federal Building investigated the 1995 bombing and the 1993 World Trade Center bombing, CNBC’s The News with Shepard Smith said.

“What we’re looking for is the trigger that caused the building to collapse, and then see how the things that may not have been perfect can contribute to that collapse,” added Kilsheimer. He is the founder of KCE Structural Engineers in Washington, DC

Two months before the 12-story Champlain Towers South residential complex collapsed, the apartment’s president sent a letter to residents warning them of structural problems. She pointed to “concrete deterioration” in the building’s parking garage and elsewhere “accelerating” and the damage had “got significantly worse” since an inspection three years ago. During that 2018 inspection, the engineer found cracked pillars, beams and walls in the parking garage and “major structural damage” under the pool.

As of Tuesday evening, 12 people have been confirmed dead and 149 more remain missing.

Kilsheimer told host Shepard Smith that he still doesn’t have a working theory about what caused the collapse.

“The bottom line is that in a situation like this there are a lot of things you have to be careful about, and it’s going to take a long time to get enough information to do all of that, and we’ve just started that process,” he said.