Tragedy in Fort Hood

Lucy Hamlin and her husband, Spc. Timothy Hamlin, wait for permission to re-enter the Fort Hood military base, where they live, following a shooting, April 2, 2014.

A soldier being treated for mental health issues opened fire Wednesday with a semiautomatic weapon at Fort Hood, killing three people and wounding several others before taking his own life as a military policewoman confronted him, officials said.

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Krystina Cassidy, left, and Dianna Simpson attempt to make contact with their husbands who are stationed inside Fort Hood while standing outside of the Bernie Beck Gate, in Fort Hood, Texas, April 2, 2014.

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Bob Gordon works on a memorial for the victims of Wednesday's shooting at Fort Hood, April 3, 2014, at Central Christian Church in Killeen, Texas.

Ivan Lopez

Investigators are focusing on the service and medical history of the Fort Hood shooter, who, according to CBS News sources, is Army Spc. Ivan Lopez, 34, seen here in an undated photo from his Facebook page.

Ivan Lopez

Investigators are focusing on the service and medical history of the Fort Hood shooter, who, according to CBS News sources, is Army Spc. Ivan Lopez, 34.

Ivan Lopez

Lopez served in Iraq for four months in 2011. As far as sources know, he was not injured or wounded in action, but when he came home he told his military superiors he had suffered a traumatic brain injury, so he was being evaluated for post-traumatic stress disorder.

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General Mark Milley, III Corps and Fort Hood Commanding General, speaks to press during a press conference about a shooting that occurred earlier in the day at the Fort Hood Military Base, April 2, 2014.

Milley confirmed that four people were dead in the shooting, including the gunman himself.

Ivan Lopez

Photograph of Army Spc. Ivan Lopez from his Facebook page.

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General Mark Milley, III Corps and Fort Hood Commanding General, speaks to press during a press conference about a shooting that occurred earlier in the day at the Fort Hood Military Base, April 2, 2014.

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General Mark Milley, III Corps and Fort Hood Commanding General, speaks to press during a press conference about a shooting that occurred earlier in the day at the Fort Hood Military Base, April 2, 2014.

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A soldier watches the media as they prepare to hear General Mark Milley, III Corps and Fort Hood Commanding General, speak during a press conference about a shooting that occurred earlier in the at the Fort Hood Military Base, April 2, 2014.

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General Mark Milley, III Corps and Fort Hood Commanding General, speaks to press during a press conference about a shooting that occurred earlier in the day at the Fort Hood Military Base, April 2, 2014.

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General Mark Milley, III Corps and Fort Hood Commanding General, speaks to press during a press conference about a shooting that occurred earlier in the day at the Fort Hood Military Base, April 2, 2014.

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General Mark Milley, III Corps and Fort Hood Commanding General, speaks to press during a press conference about a shooting that occurred earlier in the day at the Fort Hood Military Base, April 2, 2014.

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Staff Sgt. John Robertson, right, waits in a parking lot outside of the Fort Hood military base for updates about the shooting that occurred inside, April 2, 2014.