Cheers at the Boston Marathon have turned to screams.

https://twitter.com/stackiii/status/323871337951162368

https://twitter.com/stackiii/status/323871666075729921

https://twitter.com/stackiii/status/323872130964025346

https://twitter.com/stackiii/status/323872520619053058

https://twitter.com/stackiii/status/323873133633343489

https://twitter.com/stackiii/status/323876198105092097

Our prayers go out to Boston and all those affected by this horrific event.

We will continue to monitor this situation and update with developments.

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Update:

More news and photos from the scene:

https://twitter.com/stackiii/status/323874497587458048

https://twitter.com/stackiii/status/323874664629817344

https://twitter.com/stackiii/status/323875185910493184

https://twitter.com/Puntarelli/status/323880232274784256

Possible fatalities:

Former Boston Police Commissioner William Bratton:

Awful.

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Update:

According to the Boston Police, two people have been killed:

More on what may have caused the explosions:

Amazing photo of first responders:

 

God bless them.

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Update:

Some outlets are reporting that a suspect is in police custody.

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Update:

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Related coverage:

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Sickening: Alex Jones calls Boston Marathon bombing a ‘false flag’ operation

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Jackassery: NYT’s Nick Kristof can’t wait to politicize Boston Marathon bombing