The Red Cross was quickly overwhelmed with the response to its blood drive in Dallas following an ambush that killed five police officers and wounded seven more.

So many people showed up that organizers had to turn some people away.

The first donor was a police officer, the Red Cross said. 

The Red Cross said that the blood drive was planned ahead of last night's tragic attack.

Sergeant Bronco McCoy, pictured above, said he wasn't planning to donate until this morning. He was among many officers who stepped up to help.

Police officers who show up automatically go to the front of the line.

"I knew some of the officers, officers that obviously were involved in the whole thing last night," Police Cpl. Charlie Clemmons told CBS Dallas.

"I work at headquarters presently. Least I could do when they put out a call."

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