convention, today there was word of a mysterious discovery just one mile of the site. Bricks left on the roof of a building, officials calling it suspicious. And tonight across tampa, police are on... See More
convention, today there was word of a mysterious discovery just one mile of the site. Bricks left on the roof of a building, officials calling it suspicious. And tonight across tampa, police are on alert. Here's abc's senior justice correspondent pierre thomas. Reporter: Tampa police and authorities are planning for the worse, planning on an anarchy group that may try to disrupt it. You can see police here some on horses as they protect up protesters. Today, police confirm this troubling incident. Someone made their way on this roof to store bricks possibly to throw off at convention attendees. There's those that come here bent on disruption those are the individuals we will deal with individually, those are the individuals that left those items on that rooftop. Reporter: Nothing is to be overlookeded. Airspace is being restricted. Streets will be closed and contingencies for mass casualties are in police. They told abc they have identified no notice about disruptions. Like this in the 2008 party convention in denver and minneapolis are anticipated. Someone planning on being affiliated with the group anonymous has posted this online, saying members will be in tampa. Authorities are concerned not only about the convention site but locations throughout tampa.
This transcript has been automatically generated and may not be 100% accurate.