The Brussels terror attack: What we know about the investigation so far

At least 31 people were killed in the Belgium capital of Brussels following two separate attacks by ISIS.  The group claimed responsibility for the massacre, carried out at Brussels International airport and Maelbeek metro station Tuesday morning.Here's what know so far about the investigation:- A security camera photo of three unidentified men was published by Belgian media outlets who police suspect are behind the bombings. The picture shows three men wi