The unfinished pedestrian bridge dubbed a “construction marvel” at Florida International University (FIU) was undergoing a “stress test” at the time of its collapse on Thursday.

According to the Associated Press, workers were tightening suspension cables — meant to ensure that the overpass could withstand a sufficient amount of weight and pressure — as part of the test when the bridge buckled. State and federal investigators found that the extra tension on the suspension cables may have been a factor in the lethal collapse, which left six dead and 10 injured.

The innovative bridge was designed by a team at FIU. The team employed the Accelerated Bridge Construction (ABC) technique, making the Sweetwater bridge the first to be built with this method. By using ABC, contractors were able to work without blocking the street below. A fact sheet released by FIU touted the bridge’s 100 year lifespan and ability to withstand a Category 5 hurricane.

Given these lofty expectations, the collapse came as a real shock to the FIU community. Following the tragedy, Figg Bridge Design, one of the contractors tasked with erecting the bridge, released a statement underscoring the shocking turn of events.

“In our 40-year history, nothing like this has ever happened before. Our entire team mourns the loss of life and injuries associated with this devastating tragedy, and our prayers go out to all involved,” the statement said.

The ABC method requires workers to lift the already constructed bridge into place.

Although the stress test may have played a role in the collapse, investigators and experts warn that it’s too early to understand all of the variables at play. Because the Sweetwater bridge employed state-of-the-art design methods, it’s unclear if design errors, construction failures, or a combination of both are to blame.

Unfortunately, uncertainty comes along with innovation, as U.C. Berkeley engineering professor Robert Bea told the Associated Press.

“Innovations take a design firm into an area where they don’t have applicable experience,” Bea said. “We have another unexpected failure on our hands.”