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(WXIA) -- The lone shooting suspect who took the lives of 12 people in Washington DC's Navy Yard Monday has a criminal record in DeKalb County.

Alleged gunman Aaron Alexis was killed in Monday's shooting rampage. It remains unclear exactly how he died, but authorities said he was killed after a gun fight with police.

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The Navy Yard was still an active crime scene Tuesday morning after the deadly shooting spree. Investigators say 34-year-old Alexis acted alone and they are learning more about his troubled past.

CNN Correspondent Emily Schmidt reported from Washington, DC, where investigators continue working to find out why Alexis entered the Navy Yard and started shooting.

A witness there said Alexis came around a corner, aimed a gun and fired at least two or three shots.

The Navy Yard shooting victims range in ages from 46-to-73. None of them were military personnel. All were civilians or contractors.

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Alexis was a contractor. He began working at the Navy Yard just one week prior to the shooting, which gave him access to the Navy Yard grounds.

Friends of the gunman said he had worked at other Navy offices over the summer, and may have been frustrated about his pay. But they said they never expected him to open fire on Monday.

Alexis was in the Navy's Ready Reserve. A United States offense official said he was discharged following a pattern of misconduct.

Court records show Alexis was arrested in 2004 in Seattle for shooting out the tires of a car. Alexis told detectives this was an anger-fueled blackout.

He was arrested again in 2008, this time in DeKalb County. The police citation says he was inside a club on Chamblee Tucker Rd, when he was kicked out cursing, after damaging some furnishings.

He spent two days in jail before posting bond. The only ties Alexis appears to have with the area is a family member.

On Tuesday, two FBI agents visited that home in Acworth. They knocked on the door and walked around the home, but no one came out.

Agents would only say they were hoping to talk with "someone" regarding the DC shooting.

Tuesday morning, DeKalb County Police Chief Cedric Alexander talked with 11Alive's Karyn Greer about that history.

"Our records reflect back on August 10, 2008 that he was arrested in DeKalb County for disorderly conduct and it appears he might have spent a night in jail but ended up for forgiveness bond on a county ordinance," Alexander said.

The records do not reflect a weapon was part of the disorderly conduct charge.

"Let's be mindful it was a low level case, a county ordinance" he said, "but it appears to follow a pattern as this case continues to involve some history that I think is becoming very questionable for all of us."

If any warrants would have been issued before that arrest, Alexis would have been held longer. Alexander said when he was arrested in DeKalb County and forfeited the bond, that was the last police heard of him.

"Our engagement with him was very early. We don't know what his history was before he came into DeKalb County," Alexander said.

He said authorities in Washington, DC have not contacted the DeKalb County Police Department, but that the force is ready to help out and work very closely with them to further identify Alexis or anyone else who may have been involved with Monday's Navy Yard tragedy.

In 2010, he was arrested for firing a gun through his apartment ceiling. Alexis said he was cleaning the gun when it went off.

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