Staff Sgt. Adam Arndt, the U.S. Army recruiter who shot and killed 17-year-old student Michelle Miller before turning the gun on himself Monday, was romantically linked to his victim, friends of hers say.

Arndt, 31, was married to 21-year-old Army recruit Kaitlyn Arndt but was known to have romantic contact with teenage girls on Facebook and through text messages, the Washington Post reported Wednesday, citing friends of Michelle.

But Arndt’s mother-in-law told the paper that the couple appeared to have a solid relationship.

“They seemed like a great couple,” said Kaitlyn’s mother, Paula Schum, who noted that they were considering starting a family. “It just seemed like such a whirlwind. It’s just such a shock and such a horrible thing.”

Arndt was found dead of a gunshot wound Monday morning in his home in Germantown, Md. Michelle, a senior at Rockville High School, was also found dead in the home, where authorities found a handgun.

The 17-year-old high school student had planned on entering the U.S. Army Reserves after graduation, according to CBS News. It’s unclear how Arndt and Michelle met, but the recruiter’s territory included Rockville High School.

Her father, Kevin Miller, said his daughter was “a little smitten with this guy,” referring to Arndt. He told CBS News that Arndt and his daughter met about four or five months ago.

Army policy forbids recruiters from fraternizing with recruits, including dating or having any type of personal relationship.

A vigil was held for Michelle at Rockville High School on Tuesday, where friends said she was strong, fun-loving and driven, according to MyFoxDC.com.

Miller said his daughter planned on using her military pay to pay for college.

"She had her life taken away from her in one fell swoop," he said.

Arndt was a native of Manitowoc, Wis., and joined the Army in October 2003. He was deployed to Turkey from September 2009 through September 2010 and received a medal for his service in the war on terrorism.

The 31-year-old Army recruiter started working in the Gaithersburg, Md., recruiting office in January 2011.

Kaitlyn Arndt’s family said there were no signs that Arndt was about to commit such a crime.

“I’m in total disbelief,” Kaitlyn’s father, Randy Schum, told the Post. “This is unbelievable.”

The Army said it’s unsure whether the murder-suicide will compel it to look over its recruiting methods.

“The only thing the Army can do at this point, because there is an investigation, is express that the battalion is deeply saddened by the loss of Staff Sgt. Adam Arndt and Michelle Miller,” Army spokesman Mark Rickert said.

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