A 15-year-old accused of raping a woman on an Olney playground told the victim that she would “end up on the bottom of the Potomac River” if she didn’t comply, according to arrest records, as new details emerged Tuesday about the attack last month.

Alvick Omenga, a high school freshman, appeared at a Montgomery County District Court hearing via video feed from the county jail. His dark-green prison jumpsuit engulfed his shoulders, and he looked with wide eyes into the camera. Judge J. Michael Conroy told him that if convicted he faced possible life in prison and ordered him held on $5 million bond.

Montgomery police arrested Omenga on Monday and charged him as an adult with first-degree rape and attempted robbery. His family members could not be reached for comment. Prosecutors said he had run away from home more than two months before the attack. School officials said he had enrolled this year as a freshman at Sherwood High School in Sandy Spring but was not an active student.

His writings on Facebook appear to be those of a typical teenager. A student with an e-mail address tied to Omenga’s name ran for class president under the name “Alvick the Champ,” according to a Facebook page devoted to the campaign.

Police allege that the teenager raped a 22-year-old woman Aug. 5 in Olney, about 10 miles north of the Capital Beltway.

At 12:40 a.m., the woman parked her car in the 18000 block of Wagonwheel Court, police said. After she got out, Omenga “blitzed” her from behind, according to arrest papers filed in court and signed by Detective Stephen Matthews.

“Don’t make a noise and you won’t get hurt,” he said, according to Matthews. “Shut up and stop talking . . . give me cash.”

The woman said she could get money from her house.

“You will give it to me first,” the suspect responded, according to Matthews.

Police allege that the suspect then grabbed the woman by the neck and forced her to a nearby playground.

As he raped her, he told her to stop crying, according to charging papers. Then he ran away, and the victim called police.

Detectives later spoke to an individual with a startling tale: Earlier in the summer — about about a week before the rape — Omenga had approached the individual, Montgomery prosecutor Peter Feeney said in court Tuesday.

“Hey, do you want to rape those two girls? It’s okay, people rape girls all the time and never get caught,” Omenga said, according to Feeney.

The person rejected the offer, but detectives got a sample of Omenga’s DNA on Sept. 9. Two weeks later, test results matched it to the Aug. 5 attack, authorities said.

Staff researcher Jennifer Jenkins contributed to this report.