And also next tonight we have new details about that other mass shooting, the terrorist attack on the shopping mall in kenya. We are told tonight that the terrorists had a secret place inside the mall... See More
And also next tonight we have new details about that other mass shooting, the terrorist attack on the shopping mall in kenya. We are told tonight that the terrorists had a secret place inside the mall for months where they could plan their attack. Abc's alex marquardt brings us the late breaking deals. Reporter: The terrorists who strode calmly through westgate mall, gunning down innocent civlians, knew the lay of the land. A kenyan official told abc news that for at least three months, the group rented a store in the mall, a base to plan their bloody attack and, according to american officials, likely stash automatic weapons and homemade bombs. The store was on the second level, above international brands like converse and samsung and near that large supermarket where we saw scenes like this. Kenyan officials say the terrorists first move on saturday was to take over the mall's control room, giving them eyes everywhere and the knowledge they were in control. They were walking cashally as if nothing is happening. No emotion. No emotion or nothing. Just a stone face and they didn't appear like they were bothered. Reporter: Among the many questions tonight is whether some terrorists might have slipped out in the mayhem, possibly trying to leave the country. Now four days after the attack first started kenyan authorities are stepping up security all along the country's borders and here at kenya's main international airport. Ten suspects are now in custody and today international forensics teams entered the mall looking for any clues about who exactly was behind the terror. Alex marquardt, abc news, nairobi.
This transcript has been automatically generated and may not be 100% accurate.