A seven-month investigation into the murder of 15-year-old Carolyn Virginia Oberman of Upper Marlboro ended last week with the arrest of a Marine stationed in California. Prince George's County detectives said they had discovered that the Marine had given inconsistent accounts of his stay in the victim's neighborhood.

Oberman, a La Reine High School sophomore, vanished the night of June 27, after she finished washing the dinner dishes and went for walk in her quiet suburban neighborhood. Her father found her strangled body near their house on North Village Drive the next day.

The Marine, 22-year-old Orlando N. Hamilton, who was on leave visiting his family on West Village Drive last summer, was charged Jan. 24 in San Diego with first-degree murder after Prince George's detectives traveled there to question him.

Over the past seven months, police had said they were frustrated with the paucity of leads in the Oberman case, but Detective Thomas Jensen said he sensed all along that the answer had to be under his nose.

"You figure that neighborhood was pretty tight," he said, noting that residents were on the lookout for strangers, but did not remember seeing anyone unusual before Oberman was killed.

Capt. Leo Rossiter, head of criminal investigations, said that in the absence of new information, detectives began combing back through evidence already collected. During that process, Rossiter said, "They found some inconsistencies in Hamilton's statement."

Jensen, the primary investigator in the case, said he learned something about Hamilton's background that raised a red flag in his mind. A few weeks ago, Jensen decided to interview the Marine again, so he contacted the Marine Corps and asked them to trace him. Hamilton was located at a Naval air base in San Diego, where he is an instructor at an artillery school, Jensen said.

Last week Jensen and another investigator, Lin Philbin, flew to California to question Hamilton. They said they had gathered enough information to charge him with first-degree murder. However the motive remains a bit murky, police said.

Carolyn Oberman's father, Martin, a supervisor at The Washington Post's Southeast printing plant, found his daughter's body in a wooded lot a half-block from the family's home the day after she disappeared. Oberman's neighbors and friends raised $25,000 in cash and pledges for a reward leading to information about the killer.

About $5,000 in cash that was collected will go to the family, police said. The pledges will not be collected.

Last week Carolyn's mother, Betty Oberman, said police officers had come to the house the night of Hamilton's arrest to tell her husband about it.

While she remembered that police were convinced that the killer had not come from outside the neighborhood, "It was quite a shock to us" when they learned that a neighbor had been arrested.She said she did not know the Hamilton family