An Afghan defense official said on Wednesday that the Afghan who opened fire on a high-ranking delegation visiting a military complex in Kabul, killing U.S. Major General Harold Greene, had served in the army for three years.

Maj. Gen. Harold Greene, believed to be the highest-ranking U.S. military officer to die in Afghanistan since 2001, spent about four years leading two major organizations at Aberdeen Proving Ground.

General Greene, 55, was shot and killed Tuesday in an attack near Kabul. He was deputy commanding general for the Combined Security Transition Command-Afghanistan.

The shooter, believed to an Afghan soldier, was killed in the attack, and 15 others were wounded, including a German general, according to Chicago Tribune and wire reports.

Prior to his deployment to Afghanistan, General Greene led the Research, Development and Engineering Command, or RDECOM, at APG from 2009 to 2011. He was then program executive officer for Intelligence, Electronic Warfare and Sensors from 2011 to 2012, APG spokesman Kelly Luster said.

"He led those organizations, so that is pretty significant," Luster said.

During his time in Aberdeen, General Greene made a major impact on those who knew him, Roger Teel, the spokesman for RDECOM, said Wednesday.

"The members of the command who knew him were devastated by the news and we are all a little shell-shocked. This kind of brought the hostilities in Afghanistan to our doorstep," Teel said.

Teel said the mood around the Aberdeen command has been very sad since they learned about General Greene's death.

"It fills you with sadness, it really does, because he was the life of the organization," Teel said, calling General Greene "a source of inspiration for a lot of people."

General Greene was a native of New York and was commissioned as an engineer officer in the Army in 1980. He had deployed to Iraq as well as Afghanistan.

"He was a man of great vision but he was down to earth. He never forgot the soldier," Teel said, noting it is very unusual for someone of his rank to be killed in this way.

"We are just all surprised," he said.

The post does not have anything formal planned to honor the memory of General Greene at this point, other than prominently featuring him in the post newspaper the APG News, Luster and Teel said.

"I know that his legacy is a great one here. He was a smart man, he knew systems engineering; he knew where this command was heading," Teel said. "He was just a special person, he really was, because he made you feel good about what you were doing."

General Greene had maintained his ties to the Aberdeen community and spoke to the Aberdeen Chapter of the Association of the U.S. Army when he was in the United States in May, according to Tamera Rush, president of TENAX Technologies in Havre de Grace and president of the AUSA chapter.

General Green also sent the local AUSA chapter a handwritten note from Afghanistan in February, thanking members for their continued support and for sending boxes of treats.

His note also talked about his mission and the effort to transition the country to its own defense.

"We are making noticeable progress in developing the [Afghan National Security Force]," he wrote. "You should be especially proud of the people – service members, government civilians and contractors – dedicated to improving the ANSF. They are true patriots and remarkably capable."

"Your donations greatly improved the morale of these great patriots," the letter concluded. "Thank you for thinking of us."