A man who had argued with his estranged wife over the custody of their three children has confessed to drowning them in a hotel bathtub on the night they were to go back with their mother, police said Monday.

Mark A. Castillo, 41, of Rockville, was charged with first-degree murder and child abuse after his release from a hospital where he was treated for self-inflicted cuts to his neck, police said.

Police did not cite a motive.

But Castillo''s wife wrote in court documents that her husband had threatened to make her suffer by killing the children. She sought a protective order December 25, 2006, and asked that the court order Castillo to receive counseling.

"He has never actually hurt [the children], but did tell me that the worst thing he could do to me would be to kill the children and not me so I could live without them," she wrote in the petition.

She also wrote that when her husband took the children for visits, he would not tell her where they were staying.

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A temporary protective order was approved three days after the petition was filed, but Circuit Judge Joseph Dugan rejected a permanent order January 10, 2007. In explaining his decision, Dugan wrote there was "no clear or convincing evidence that the alleged acts of abuse occurred."

Police identified the children as Anthony, 6, Austin, 4, and Athena, 2.

Castillo, of Rockville, Maryland, and the children spent time Saturday afternoon at Baltimore''s Inner Harbor, then checked into the Baltimore Marriott Inner Harbor. The children were drowned, one at a time, in the tub that night, Police Commissioner Frederick Bealefeld said. Watch police describe what they found in hotel room ยป

Police said Castillo called the hotel front desk Sunday afternoon, saying he''d killed the children and was going to commit suicide. Baltimore police and firefighters were sent to their 10th-floor room and discovered the bodies, Bealefeld said.

Castillo was supposed to have returned the children to their mother in Silver Spring at 8:30 p.m. Saturday. His wife called Montgomery County police shortly after that time to say that her husband had not returned the children, Bealefeld said.

Baltimore police did not know how Montgomery County police responded, but said the cases were not connected until after the children''s bodies were found.

Bealefeld wouldn''t discuss the crime scene in detail but said police seized a laptop from the hotel room and were searching Castillo''s home.