revelations were all part of the videotaped confession, prosecutors say, cullin jr gave police over several hours. one prosecutor says dennis cullin jr's confession holds back little, telling police in vivid detail how he drowned his 63-year-old mother in the backyard pool of their lloyd harbor home. >> mrs. cullin was one of the nicest ladies i ever enun the whole thing is a tragedy. >> reporter: two family friends say cullin jr had a long history of mental illness. when he stopped taking his medication, prosecutors say, his mom confronted him on wednesday, prompting the alleged attack. >> he put her in a head lock, walked from the shallow end of the pool with her in a head lock to the deep end all the time while she was struggling. >> reporter: the prosecutor says that water struggle was violent.

revelations were all part of the videotaped confession, prosecutors say, cullin jr gave police over several hours. one prosecutor says dennis cullin jr's confession holds back little, telling police in vivid detail how he drowned his 63-year-old mother in the backyard pool of their lloyd harbor home. >> mrs. cullin was one of the nicest ladies i ever enun the whole thing is a tragedy. >> reporter: two family friends say cullin jr had a long history of mental illness. when he stopped taking his medication, prosecutors say, his mom confronted him on wednesday, prompting the alleged attack. >> he put her in a head lock, walked from the shallow end of the pool with her in a head lock to the deep end all the time while she was struggling. >> reporter: the prosecutor says that water struggle was violent. surprised him because his mom was only about 5'2". he dumped her body by a shed. >> he hasn't been convicted of anything. he hasn't said "i'm sorry." >> cullin jr's lawyer entered a not guilty plea for the young man who lived with his parents on this sprawling property. neither his father or three sisters appeared with him in cou