A Maryland man calmly described to detectives how he methodically drowned his three young children by holding them underwater in a hotel bathtub for 10 minutes each — a confession that was recorded by police and played in court Wednesday.

Mark A. Castillo, 43, of Rockville faces trial on three counts of first-degree murder in the March 2008 deaths of his children: 6-year-old Anthony, 4-year-old Austin and 2-year-old Athena. His attorneys contend that he is not criminally responsible for the slayings — Maryland's version of an insanity plea.

Castillo's attorneys are trying to prevent his two statements to police from being admitted as evidence at trial. Prosecutors played a tape of the first of those statements for the judge Wednesday to verify its authenticity. The jury has not yet been chosen.

Asked by homicide Detective Raymond Yost why he killed his children, Castillo let out a long sigh before describing a custody battle with his former wife.

"We've been going through an extremely hard divorce. ... My wife had denied my visitation," Castillo said. "I felt like I didn't want them to be in this world anymore."

Castillo described how he took his children to the Maryland Science Center in Baltimore and then checked into a Marriott hotel downtown.