Paul van der Sloot, a judge-in-training on the island, was questioned for two hours Sunday afternoon after five hours Saturday night, said Police Superintendent Jan van der Straaten.
Joran van der Sloot, 17, one of the people last seen with Natalee Holloway the night she disappeared. Three other men have been detained, but no one has been charged.
Van der Straaten said the father was asked to come back Sunday because officials were not able to finish the interrogation on Saturday, but declined to give more details.
"He was questioned as a witness, no more or no less," van der Straaten told The Associated Press.
The attorney general's spokeswoman, Mariaine Croes, said witnesses are questioned when prosecutors believe they may be able to add something to the case.
"You may know something more or you may have seen something more, but you are not a suspect or thought to be part of any crime," Croes said.
"I think that he probably knows more than he's letting on," said Robin Holloway, the missing teen's stepmother, on CBS News' The Early Show.
"I was questioning the integrity of the father because he is a person that is currently in training to be a judge, but apparently his son feels that he is above the law," said Linda Allison, Holloway's aunt, also on The Early Show.
"You have a son that is out driving under the age of 18 and here, according to Dutch law, you have to be 18 to be able to drive, to gamble, to drink. And with him being 17 years of age, he's done all of those things," Allison told Early Show co-anchor Hannah Storm.
"I don't know if he would be arrested, but I would feel like he would at least know some key information as to when his son arrived home," she added.
During Sunday's interrogation, van der Sloot's wife, Anita van der Sloot, met with Joran in jail, said van der Straaten.
Holloway, 18, of Mountain Brook, Ala., disappeared in the early hours of May 30, the last day of a five-day vacation with 124 students celebrating their high school graduation. Her U.S. passport and packed bags were found in her room.
Joran van der Sloot and two friends said they took Holloway to a northern beach but dropped her off at her Holiday Inn, where they claim she was approached by a security guard.
On Saturday, a judge ordered Joran van der Sloot and his two friends, brothers Deepak Kalpoe, 21, and Satish Kalpoe, 18, to stay in jail for at least another week while the investigation continues.
CBS News Correspondent Kelly Cobiella reports that they have been moved to a prison on the southern end of the island where they'll stay for at least another week.
A fourth detained man — a party boat disc jockey — was to appear before a judge Monday, Croes said. He was identified by his boss as Steve Gregory Croes, 26.
Steve Croes was arrested Friday after giving police a statement, said Marcus Wiggins, his boss on the boat Tattoo. Steve Croes is not related to Mariaine Croes.
It was not known how the disc jockey might be connected to the case.
Cobiella reports that the co-owner of the boat, Marcus Wiggen, says Croes knows one of the suspects from an internet café, but it is not clear if he knows the Dutch suspect.
"I would never expect that he would be anywhere close to this investigation," Wiggen said.
Under Dutch law, which Aruba follows as a Dutch protectorate, authorities can detain people for up to 116 days without charging them.
Investigators refuse to say whether they believe Holloway is dead. Her mother, Beth Holloway Twitty, has said she will continue to believe the teen is alive until she has proof to the contrary.
Holloway Twitty, 44, sat in the front pew during a Saturday night Mass dedicated to her family at a Pentecostal church.
"We admire the strength and courage you've shown as a mother," pastor Gilbert Martes told the Holloway Twitty, who listened to the sermon with her eyes closed.
Holloway Twitty has insisted that Joran van der Sloot and the Kalpoes hold the key to the investigation and that authorities pressure the young men harder to tell the truth.
CBS News Correspondent Peter King reports that Holloway's family searched the southeast area of the island known for its caves during the weekend, but her father admits that right now, in his words, they're just grasping at straws.
"It is 22 days now and it is a slow process," said Robin Holloway. "I know they're working around the clock on it, but it is frustrating"
"Every day without Natalee is very frustrating to not know where she is or to know what has happened or if she's elsewhere on the island," Allison added.
In Alabama, a Holloway family friend said Holloway's relatives identified and located Joran van der Sloot and the Kalpoe brothers less than a day after the teen vanished. But the three young men were not detained until 10 days later.
"It's just disappointing that they (authorities) weren't able to move faster," Jody Bearman, who organized the graduation trip, told AP.