NEW YORK (CBSNewYork/AP) — The slaying of five police officers in Dallas in an attack blamed on snipers was the deadliest day in U.S. law enforcement history since the Sept. 11, 2001 terrorist attacks, according to a memorial group.

Four Dallas police officers and one Dallas Area Rapid Transit officer were fatally shot Thursday night. Seven other officers were wounded in the Dallas attacks.

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The National Law Enforcement Officers Memorial Fund, which monitors the deaths of officers, reports 72 officers were killed as a result of the 9/11 terrorist attacks on the U.S. The group labels that attack as the deadliest day in U.S. law enforcement history.

Gunfire broke out in Dallas during protests over this week’s fatal police shootings of two black men in Louisiana and Minnesota.

Police believe the snipers were aiming at officers as retaliation over the controversial police shooting deaths of 32-year-old Philando Castile and 37-year-old Alton Sterling.

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Castile was killed during a routine traffic stop outside of Saint Paul, Minnesota. The aftermath was captured and streamed live on Facebook by his girlfriend.

And in Baton Rouge, Louisiana, police officers shot and killed Sterling in a convenience store parking lot where he was selling DVDs, which was also captured on cell phone video.

A suspect in the Dallas attack said he was upset over recent police shootings of black men and wanted to kill white people, Police Chief David Brown said Friday. Brown said the suspect made the comments before he was killed during a standoff with police in a parking garage.

President Barack Obama said America is “horrified” over the Dallas shootings and there’s no possible justification for the attacks.

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