Washington state authorities cleared one of the five companies involved in the South Lake Union construction project where a tower crane collapsed in late April, killing four.

The state Department of Labor and Industries said Monday it formally closed its investigation into Seaburg Construction and found no violations, according to spokesman Tim Church. The company had provided the personnel that operated the tower crane and wasn’t involved in dismantling it — work that was underway when it collapsed.

The state agency is continuing its investigation of four other companies: general contractor GLY Construction, subcontractors Northwest Tower Crane Service and Omega Morgan, and crane owner Morrow Equipment. Authorities have been tight-lipped on the investigation, but some experts believe based on available images and video footage that the crane collapsed as a result of prematurely removing the bolts that fasten its sections together.

News of the closure of the inspection of Seaburg came a day after a crane collapsed in Dallas, killing one person and injuring five others. The collapse in Seattle, also on a blustery day, killed two ironworkers and two passersby.

Tower cranes, which have dominated Seattle’s skyline in recent years amid its building boom, have operated safely for years. Before the collapse in April, the last fatal accident involving a tower crane locally was in 2006.