The bodies were discovered after the man called hotel security about 1:15 p.m. from his 10th-floor room at the Baltimore Marriott Inner Harbor at Camden Yards, saying that he had killed his children and was considering harming himself, said Officer Troy Harris, a city police spokesman.
Their father, identified by police as Mark Castillo, 41, was taken to University of Maryland Medical Center with what appeared to be minor self-inflicted cuts, authorities said.
Sterling Clifford, a police spokesman, said homicide detectives are investigating the possibility that the children were drowned, suffocated or strangled. Clifford said they were not shot or stabbed.
"There is some evidence that something happened in the bathroom. What that is, I do not know," he said late last night. Detectives were awaiting autopsy results. Clifford said it was likely that Castillo would be charged overnight.
Police executed a search warrant yesterday at Mark Castillo's home in Montgomery County.
Castillo's estranged wife, Amy Castillo, also lives in Montgomery County, a police source said. She was interviewed by detectives last night.
Mark and Amy Castillo were separated, and online court records indicate that they have been involved in a long-running custody battle in Montgomery County.
In the Silver Spring neighborhood where Amy Castillo lives on Waterford Road, the lights were on throughout a two-story brick house, though no one responded to knocks on the door. A shattered window by the door was held together with duct tape.
Neighbors, just learning of the news, reacted with horror. One next-door neighbor who identified herself as a friend burst into tears, sank down in her doorway and sobbed upon hearing about the deaths.
The news generated similar dismay in Baltimore. Mayor Sheila Dixon slipped out of a community meeting at a Little Italy restaurant yesterday afternoon to take cell phone calls about the dead children. She returned minutes later and spoke with emotion in her voice.
"There are some things we have no control over," she told the crowd of about 100, referring to the killings.
Dixon and Police Commissioner Frederick H. Bealefeld III are expected to hold a news conference today at police headquarters.
Clifford, the police spokesman, said Mark Castillo seemed to have "some history" of domestic violence. Court records show a domestic dispute between him and Amy Castillo in December 2006.
They had been sharing custody of three minor children since mid-2006, when Amy Castillo filed divorce papers, according to court records. A judge had ordered that Mark Castillo's visits with the children be supervised.
In September 2006, a Montgomery County circuit judge ordered that Mark Castillo undergo a psychological review, and later court entries show that he was undergoing therapy. But that December, when domestic violence issues emerged, a court ordered that Mark Castillo leave the home and have no contact with Amy Castillo.
In June 2007, Amy Castillo filed an emergency motion to prevent Mark Castillo from having access to the children, records show. The outcome was unclear, but Mark Castillo filed motions to enforce a visitation agreement. Another court date was set for May.
Lt. Paul Starks, a Montgomery County police spokesman, said "there was an active agreement for visitation, and he and she were working with that." He added that county police had "a limited role in this."