There are some New York stories that are almost too horrible to tell. This is one of them.

It is a story rife with drugs and alcohol, repeated sexual abuse, beatings, and murder. It takes you deep into the chilly hearts and twisted minds of some of the cruelest humans on earth – and makes you suspect the worst about everyone.

The stage is a cavernous courtroom on the 10th floor of the Criminal Court building in Brooklyn, State Supreme Court Justice Gus Reichbach presiding.

At the defense table is a short, muscular man named Mickey Cass, whose well-developed biceps and chest are so big it takes two sets of handcuffs to get his arms behind his back.

Mr. Cass, who wears close-cropped hair and has a prison-pale complexion, is a suspected serial killer of gay men. He is on trial in Brooklyn on charges of strangling his roommate, Victor Dombrova, on September 25, 2003. He awaits trial in Buffalo for murdering Kevin Bosinski in July 2002.

Mr. Cass, 26, does not deny either slaying: He admitted both on a startling police videotape last year. He is presenting a novel defense: Years of horrific sexual abuse at the hands of his father caused him to snap when the men made passes at him.

Extreme emotional disturbance is the name of this defense and, in reality, the best Mr. Cass can hope for is to be acquitted of second-degree murder, which carries a life sentence, and convicted of first-degree manslaughter, with a maximum of 25 years.

It’s a risky defense, because it allowed the prosecution to tell the jury about the Buffalo case but, as Judge Reichbach told Mr. Cass in court yesterday, it’s probably his best shot.

The defense took its best shot yesterday with testimony from Sanford Drob, a forensic psychologist who spent nearly 20 years as a senior psychologist at Bellevue Hospital’s prison ward, one of the scariest places in the universe.

Using legal records dating back to 1989, when Mickey Cass was 10, Mr. Drob took the jurors on a tour into the depths of human depravity.

“From the ages of 5 to 10, Mickey Cass had been sexually abused by his father,” Mr. Drob said. The father, Caesar Locascio, was eventually convicted and sentenced to up to 18 years in prison. He died there last year after doing 12 years.

Under questioning from the defense lawyer, John Stella, Mr. Drob described in graphic detail how Locascio sexually abused his two children – Mickey and his sister – and his girlfriend’s two youngsters over and over again.

He forced Mickey to perform oral sex on him and he, in turn, performed oral sex on Mickey. Once, when Mickey was 10 and his sister 9, their evil father made them have sexual intercourse so he could watch.

There was also physical abuse – the father once slammed Mickey’s head into a table, briefly blinding him in one eye.

Another time, the sicko father, apparently feeling some remorse, shot himself in the chest with a .22 caliber pistol. Unfortunately, he survived. Mr. Drob said Locascio also started feeding his son drugs and alcohol from the age of 5.

As a result, Mr. Drob said, Mr. Cass gets “aggressive when he feels someone is threatening him or intending to violate him.” Mr. Cass, the psychologist said, also is “anti-social” and has touches of depression, paranoia, hyperactivity, and little or no impulse control. Taken from his father at age 10, Mr. Cass has bounced through several mental institutions, juvenile prisons, and drug rehab centers.

“I absolutely believe that if he did not have the life history that he has, he would not have done the things that he did,” Mr. Drob said. “He has a rage and anger far beyond what could be considered normal.”

There were some indications that this defense was getting to the jury, which will likely start deliberating today. Several jurors grimaced at the detail of abuse, two women jurors cradled their heads with their hands, and almost all of the others listened raptly.

The prosecutor doesn’t buy any of it, of course.

Assistant District Attorney Anna-Sigga Nicolazzi, a blonde version of the Lara Flynn Boyle model of prosecutors – tall, thin, and deadly serious – got Mr. Drob to acknowledge that Mr. Cass is extremely manipulative and lies a lot.

She also suggested Mr. Cass cooked up his defense in a prison law library.

It remains to be seen if the jury buys the story and shows Mr. Cass more sympathy than he showed to the men he killed.