(CNN) -- Police continued their investigation Tuesday into the shooting deaths of an Army recruiter and a 17-year-old girl in Maryland that appear to be "a murder-suicide," Montgomery County police said.
Staff Sgt. Adam Anthony Arndt, 31, knew Michelle Lynne Miller because he supervised her recruitment as she planned to enlist in the Army Reserves after graduating high school, police said.
Police found both of them dead Monday inside Arndt's apartment in Germantown while looking into a report of a missing juvenile possibly being at that location, police said. Police broke down the door because they were unable to make contact with anyone inside.
"Detectives now believe that Arndt shot Miller and then shot himself," police said in a statement. Miller was a senior at Rockville High School, police said.
Miller's father, Kevin, told CNN affiliate WJLA that he believes his daughter was lured to Arndt's residence after she received a call Sunday night from Arndt, who was threatening suicide.
His daughter raced to his home in her mother's car, her father said.
Miller had just been accepted at Arizona State University and enlisted to help pay the tuition, her father said. She wanted to be a psychotherapist, he said.
Arndt was apparently in violation of Army recruiting regulations because a recruiter isn't "allowed to have anyone who would be considered influenced by your position in the Army in your private home, in your dwelling place," said Kathleen Welker of the U.S. Army Recruiting Command.
When asked if the recruit's presence in Arndt's residence violated regulations, Welker stated: "I would say it appears that way. But it is being investigated by the police and by our Criminal Investigation Division."
A recruiter is also prohibited from having any sort of relationship with someone applying for military service, Welker said. Arndt worked at the recruitment center in Gaithersburg, Maryland, she said.