A U.S. Army staff sergeant shot and killed a 17-year-old girl at his Germantown apartment before turning the gun on himself Monday, police said.

Their bodies were found about 10 a.m. Monday after police received information that missing Rockville High School student Michelle Lynne Miller might be at the residence of 31-year-old Adam Anthony Arndt.

Miller, an honors student and varsity lacrosse player, was last seen the night before.

When no one answered at the residence on the 12900 block of Pinnacle Drive, officers forced their way inside. Both the man and girl were dead.

Montgomery County police said Michelle planned to enlist in the U.S. Army Reserves after she graduated from Rockville High in two months. Arndt was her recruiter.

News of Michelle's death spread quickly on social media. Friends and classmates expressed shock and condolences from as far as Florida and California.

"I still remember when we played soccer together and went to the mall and how you were always so sweet and welcoming," said one girl with the Twitter handle @xxicvt. "I can't even control my tears right now and I am still in shock."

"What a great teammate, en even better friend and an all together beautiful girl," wrote @hubbsie12.

School officials on Monday sent out letters to parents of Rockville High students.

"For those of you who knew Michelle, we ask that you remember and celebrate her life," the letter said. "She was currently an athlete on our varsity lacrosse team, an honors/AP student, and an active member of the Senior Class. For those of you who did not know Michelle, we ask that you respect our sadness and support us with your understanding."

Montgomery County Public Schools will work with staff members at the school to provide counseling and support to students.

Police said Miller was last seen leaving her Rockville home at about 9 p.m. Sunday.