IT'S HARD to know what's more monstrous about accused killer Mark Patrick O'Donnell.

Is it the gruesome crime to which police say the 48-year-old Plymouth Meeting man has confessed - the unspeakably violent murder of his lover's 14-year-old daughter, who authorities say was strangled with her pajama bottoms and sexually assaulted with a foreign object?

Or is it the way he allegedly tried to dispose of the 110-pound body of Ebony Nicole Dorsey, 14 - a freshman at Wissahickon High School - by stuffing it in a large plastic tub and leaving it in a wooded area next to a cousin's house?

Or is it the outrageous accusations - unsupported by any evidence - he shouted to reporters yesterday trying to place blame on his young victim, who had been baby-sitting O'Donnell's 4-year-old daughter?

"I didn't touch her sexually," O'Donnell claimed as he was being led to the awaiting wagon. "I caught her molesting my daughter."

"He'd use his own daughter as an excuse for what he did?" Matthew DelConte, Ebony's visibly shaken uncle, asked yesterday.

"That's not even a concept to believe. I know my niece, and she's not capable of that.

"He is truly a monster."

New details emerged yesterday in the 24 hours after Ebony's body was found in Whitpain Township, at the residence where O'Donnell allegedly dumped it.

Police had immediately fingered O'Donnell - who is married but is also the boyfriend of Ebony's mother - as a suspect and arrested him late Sunday night at the nearby home of relatives.

According to the affidavit released yesterday by Montgomery County prosecutors, O'Donnell killed Ebony after a long night of smoking crack cocaine at the home of her mother, Danielle Cattie.

According to the statement, Cattie told police that her boyfriend's crack binge - at her home on a modest block on Butler Pike near Maple Avenue, in Ambler - started at roughly 15 minutes past midnight and lasted until about 5:30 a.m.

O'Donnell, who had been at the Cattie residence earlier Thursday evening, already had taken Ebony and his own daughter, Kyra, back to his apartment in Plymouth Meeting so the teen could baby-sit there.

The affidavit said Cattie told police that O'Donnell was "wired" when he left the house, that he had a tendency to become violent when using the drug and that one time he had choked her, pulled her hair and thrown her to the ground.

According to O'Donnell's account later to the cops, when he arrived back at his apartment, he saw his daughter on the sofa with no potty-training pants on and Ebony bending over to change them.

O'Donnell told detectives he yelled at Ebony - angry over her changing the pants in the middle of the night - and then slapped her in the face.

The affidavit said that O'Donnell continued to slap and punch Ebony and that they ended up in Kyra's bedroom and "the next thing [he] realized" he had Ebony's white striped pajama pants around her neck. It said he choked Ebony until Kyra, who was awake, said "Daddy," and he realized that the teen was no longer breathing.

But the autopsy performed on Ebony on Sunday by forensic pathologist Dr. Ian Hood suggested that in addition to her death from blunt-force trauma and asphyxia, or strangulation, she appeared to have been sexually assaulted.

The affidavit said Hood found three distinct tears in the girl's anus, and deep internal bruising "consistent with penetration by a foreign object and sexual assault."

After the killing, O'Donnell told detectives, he dumped the clothes from a blue plastic tub in his room and put Ebony's body inside.

The affidavit said he initially drove to the airport with his daughter, where he was supposed to pick up his wife, but, learning her flight had been delayed, he instead went to the house of his nephew, Anthony Carter, and placed the tub in the yard there.

He then stopped at a Lukoil gas station near the Blue Route in Plymouth Meeting to dispose of Ebony's school book bag.

Later, on Saturday, he returned to the nephew's home - on Union Meeting Road in Whitpain - and attempted to cover the tub with leaves and sticks.

O'Donnell was arrested shortly after 10 p.m. Sunday, at another residence belonging to relatives, where police found him hiding under a comforter in a room on the second floor.

At a preliminary arraignment hearing yesterday afternoon before Justice Francis J. Bernhardt in his Conshohocken offices, O'Donnell - in bare feet and shackled at the waist and ankles - appeared defiant.

"I loved her and never meant for this to happen," O'Donnell said.

Afterward, he said he never smoked crack and wasn't high at the time of Ebony's slaying.

"By everyone's account, [Dorsey] was a terrific young woman, and well-liked," Montgomery County Assistant District Attorney Risa Vetri Ferman said. "The death she suffered . . . was an absolute tragedy."

Crime-scene investigators spent hours combing through O'Donnell's apartment in search of evidence.

On the quiet, tree-lined block, people prefer to keep to themselves, said Tom Gibbons, a resident of the same building. Gibbons, 80, said he didn't know O'Donnell, but that he was shocked at the news.

"The way people are over here, I'm not surprised I didn't hear anything," he said.

At the house where Ebony lived, Cattie did not speak to reporters and was said to be busy making funeral arrangements.

When asked how she feels about Ebony's death, an unnamed family friend responded: "There are no words . . . " *