At least seven of those killed were students at Plaza Towers Elementary School in Moore. The twister, which measured 2 miles at one point, has been given a preliminary classification of an EF-4 tornado (winds of 166 to 200 mph), according to weather officials.

UPDATE 9:28 p.m. EST: At least 51 people were killed in the storm, including seven children from Plaza Towers Elementary School in Moore, according to KFOR in Oklahoma City. The news station reported that 75 student and staff were inside the school when the storm struck. Officials said Monday night that the search of the rubble remaining of the school had turned to a recovery mission.

The explosion occurred at the West Fertilizer Plant shortly before 8 PM CT

This will be the last update of this article this afternoon. There is a press conference with the FBI at 5P, after which we'll publish a new article recapping the details. What we do know as fact is that the FBI and has made "significant progress" in this investigation.

UPDATE @ 3:02:

The Boston police department has tweeted that there HAS NOT been an arrest made:

UPDATE @ 2:51:

CBS News is reporting that the suspect is a WHITE MALE not 'dark skinned' as previously reported by other outlets:

Additionally CBS News is reporting that cellphone tower data was used to find the bomber:

AP just tweeted that "Federal officials deny that Boston Marathon bombing suspect is in custody." - however AP has NOT retracted that their source confirms so.

ABC News also has NOT reported an arrest:

UPDATE @2:29: We have conflicting reports. NBC is saying that a top official in Boston says that there is NO arrest:

However, a source at the Boston Globe continues to state that a suspect is in custody:

UPDATE @2:21: This is helicopter footage of the Federal Courthouse in that is from Twitter - AP and CNN are reporting that the suspect has been brought here. However, someone can be taken into custody without there being an arrest. No officials have made a statement regarding a suspect in custody and we are reporting based on information from CNN and the Associated Press.

UPDATE @ 2:06 PM: The AP reports that Federal Marshals have a suspect in custody and are brining him to a Federal Courthouse:

UPDATE AT 1:49: CNN REPORTS THAT A SUSPECT HAS BEEN ARRESTED AND IS IN CUSTODY.

Associated Press is also reporting that an arrest has been made:

According to reports on major national media, CNN has broken the story that the FBI has obtained clear footage of a suspect in the Boston bombings. The footage originated from a department story surveillance camera and was used to locate other footage that included images of the suspect from a Boston TV station.