As friends continued to mourn the loss of Sunshine Stewart, a Mainer who they say was in her element on the water, the state attorney general’s office said Friday that a 17-year-old had been charged with murdering her after she disappeared while paddle boarding near a remote island early this month.

The authorities identified the suspect on Friday as Deven Young, of Frankfort, Maine. A spokeswoman for the attorney general’s office said it was seeking to try Mr. Young, who will turn 18 on Sept. 24, as an adult.

His arrest in the killing of Ms. Stewart, 48, who the authorities said died from strangulation and blunt force trauma, was announced on Thursday by the Maine State Police, who did not name him or say whether he had been charged.

The police said on Thursday that they were continuing to investigate Ms. Stewart’s killing and asked for the public’s help. A motive for the killing remained unclear on Friday, and investigators did not release further details about the circumstances.

Mr. Young made his initial court appearance on Friday in Knox County, The Midcoast Villager reported. He is being held at the Long Creek Youth Development Center in South Portland, and his next court appearance is Aug. 22.

Jeremy Pratt, a lawyer for Mr. Young, declined to comment on Friday.