The person "is suspected of being involved in the disappearance of the tourist," 18-year-old Natalee Holloway, said a statement from the Aruban attorney general's office.
The latest person in custody was born on July 21, 1978, and has the initials S.G.C., the statement said, adding, "As a result of the ongoing investigation, this is all the information that can be given at this time." CBS News Correspondent Peter King reports the suspect is a man.
"A fourth arrest has been made, and his name is 'Steve,' and that's all the information that I have," Natalee's mother, Beth Holloway Twitty, told the Associated Press. "Whether or not he's involved with my daughter's disappearance, I can't wait to find out that answer."
Meanwhile, prosecutors have gone back to court to ask that three other suspects stay in jail, although they haven't been charged: 17-year-old Joran van der Sloot, the son of a justice official on Aruba, and his two friends, Surinamese brothers Deepak Kalpoe, 21, and Satish Kalpoe, 18. The three were detained on Thursday. Under the law, a judge must review their case after 10 days and decide their status.
"The process allows for a period of time for the prosecutor to do the investigation. That can go well over 100 days," said local attorney Lincoln Gomez.
A judge was expected to rule as well Friday on another petition, from van der Sloot's father, Paul van der Sloot, to be able to visit his son in jail. None of the four detainees has been formally charged with a crime.
Authorities' announcement of the arrest Friday came nearly three weeks after Holloway's disappearance in the early morning hours of May 30, the same day she was to return from a five-day trip with 124 other students celebrating their high graduation in Mountain Brook, Alabama.
"It's emotionally draining, it's physically draining,"told CBS News Early Show co-anchor Julie Chen. "Every day, we wake up, 'is today going to be the day? Please let us find Natalee.'"
On Thursday, Police Superintendent Jan van der Straaten told The Associated Press that authorities used a helicopter "to search for possible remains — but found nothing." He declined to say where the helicopter searched.
"I don't think they're going to find Natalee until these [first] three guys talk," said Robin Holloway. "They know they were the last ones to see her. And I firmly believe in my heart they know where Natalee is and just please tell us. They hold the answer.
Asked why it took investigators more than two weeks after Holloway's disappearance to search the van der Sloot home, Attorney General Caren Janssen said Thursday, "You have to build up an investigation. You can't just go in there like a cowboy, you have to give certain direction to investigators."
The Kalpoe brothers have told police that they and Joran were with Holloway and that she and the Dutch youth were petting in the back seat of their car. The detainees initially said they took Holloway to a beach on the northern part of the island then dropped her off at her Holiday Inn hotel, where they claimed she was approached by a security guard.
But Antonius "Mickey" John, a former hotel security guard released from custody on Sunday, told reporters that Deepak Kalpoe told him during a chat in jail that he and his brother actually dropped the young van der Sloot and Holloway off together near the Marriott, about 10 blocks north of the Holiday Inn. John said he passed the information on to police.
Kalpoe's lawyer would not comment on John's statement Wednesday, but said his client maintained his innocence.
Van der Straaten dismissed rumors that police may investigate coastal waters on the north side of the island known to have sharks. "Sure, we have shark places on the northern side, but they have nothing to do with the investigation," he said.