It was hardly a crime to attract much attention in a hard-bitten urban environment. Four teen-agers high on drugs and alcohol encountered two brothers, both around 30 and both drunk, in a tough neighborhood of St. Louis one November night in 1986.

Name-calling, quarreling and a rumble ensued. Three of the youths took off with a few stolen dollars. Reginald L. Powell, at 18 the eldest of the attackers, stayed behind to finish off the victims with a knife.

He was arrested the next day, tried in March 1988, found guilty of first-degree murder and sentenced to death. He is scheduled to die by lethal injection on Feb. 25 at Missouri's maximum security prison at Potosi.

But behind this seemingly open-and-shut case of murder and justice lies a remarkable story that supporters of Mr. Powell believe qualifies him for clemency and commutation of the sentence to life without parole.

His lawyer, a woman then 35 years old, became emotionally involved with Mr. Powell, who is mildly retarded, while she was preparing for the trial. Later, she had sexual relations with him in a holding cell at the state circuit court building in St. Louis.

His present lawyer, Bruce D. Livingston, a Federal public defender, says this emotional involvement contributed to mistakes that the lawyer made in presenting the case, among them not having him plead guilty in exchange for a life sentence and not putting him on the stand.

The lawyer, Mary Ann Marxkors, subsequently gave up law, but she has continued to see Mr. Powell in prison. Ms. Marxkors does not dispute the criticism and argues that in her efforts to help Mr. Powell she fell into a situation beyond her control.

''It was my first death-penalty case, and I spent a lot of time with him to gain his trust,'' Ms. Marxkors said in a tearful telephone interview from her home in St. Louis. ''I came to know a lot about where he came from, what his life had been. Yet, he was always caring toward me.

''It was such an intense sort of thing,'' Ms. Marxkors, who was a state public defender, said of the trial period. ''It became physical when the judge told me he was going to sentence Reggie to death. I went and told him, and I cried and he kissed me, and we ended up making love.''

At the next hearing, when the sentence was formally issued, they again made love in the holding room. ''It was several months before I began to ask myself, 'What the hell am I doing?' '' Ms. Marxkors said.

Mr. Powell, now 29, said in a telephone interview from the prison that he considered his death sentence unfair because his lawyer ''didn't have the skills to get me a life sentence.'' But he said they remain friends and that she visits him often.

''We are human,'' he said, ''so we all make mistakes. Unfortunately, this might cost me my life. But we don't hardly talk about what's going to happen to me.''

Ms. Marxkors added: ''I continue to see him, to write to him, to talk to him. I love him.'' She said she will be there on his execution night, if he wants her to be.

Both Mr. Livingston and Ms. Marxkors said the only hope for Mr. Powell now is that Gov. Mel Carnahan, a Democrat, will respond to Mr. Livingston's clemency petition by commuting the sentence or granting a stay of execution.

The United States Supreme Court refused in January to accept the case for review, which Mr. Livingston said ended all judicial possibilities.

Mr. Livingston, who became Mr. Powell's lawyer in 1995 as the case was going into the Federal appeals process, said that because Mr. Powell is mentally slow and has had little support from his own destitute family -- his mother and grandmother are dead -- he became unduly dependent on Ms. Marxkors, one of the few people to show long-term interest in him.

Mr. Livingston also said he was outraged that a well-educated woman of a mature age could not better handle her dealings with a vulnerable young man who ''doesn't have a real comprehension of the mistakes she made.''

Mr. Livingston also emphasized Mr. Powell's difficult childhood. ''He was born to a 14-year-old mother,'' Mr. Livingston said. ''His grandmother, who was 30, wouldn't go to the hospital for his birth because the bars were still open.''

As a child, Mr. Powell was given marijuana even before he became a teen-ager and eventually was placed in a state home for boys ''in response to the impassioned plea of a school principal,'' Mr. Livingston added.

''But he was put out a year later because of overcrowding,'' Mr. Livingston said. ''He changed schools 16 times.''

Ms. Marxkors's mental health has also played a role in the case. She said that she has been in therapy off and on for about 15 years but was not in therapy at the time of the trial. Mr. Livingston said that in the clemency petition he had tried ''to make a persuasive case that this woman is troubled.'' He said that the petition was accompanied by a videotape of her talking with an Illinois state psychiatrist.

''A stack of amazing letters from her was confiscated from Reggie's death-row cell,'' Mr. Livingston said. ''They varied in tone from that of a junior high school romance to the smutty and obscene things you might read in Penthouse or some other magazine.''

It was the discovery of those letters by prison authorities in 1988 that set off the chain of events surrounding Ms. Marxkors.

''Love and emotions can be so powerful,'' Ms. Marxkors said in her defense. ''Anyone can be blinded. The initial physical part was very emotional and driven by vulnerability and this shared thing.

''It certainly wasn't anything I ever planned.''

Ms. Marxkors was warned by the bar association that her conduct was ''inappropriate,'' but she was not formally admonished or disbarred.

Now working with troubled children while studying for a master's degree in social work, Mrs. Marxkors said she realized that there was a great gap in the way she saw Mr. Powell and his crime and the way the jury and judge looked at him and the crime.

She said she approached the case from the position that the two killings were not premeditated and that conviction would be for manslaughter, not first-degree murder.

''When I first interviewed him and noticed his retardation I thought that he couldn't even premeditate going to the bathroom,'' she said.

She also said it was not Mr. Powell who brought the knife that night, but another youth who handed it to Mr. Powell at some point in the fight, further suggesting the absence of premeditation.

Ms. Marxkors said she had not put him on the stand to testify in his own behalf and plead remorse for the killings because she had used his mental impairment as an important aspect of her defense and feared that while on the stand he might not seem as impaired as he was.

''Reggie would talk about wanting to testify,'' she added, ''but it wasn't the way I had planned to do it, so I pooh-poohed that idea. I didn't even tell him he had a right to testify.''

She said she had not tried to plea bargain for a lesser sentence because the state delayed a considerable time before making an offer and when it was made, it was for four consecutive life sentences. She opposed the offer, believing that Mr. Powell would be convicted only of manslaughter, which would have resulted in a lesser sentence.

''Even the prosecutor told me at one point not to worry so much because they would never kill this kid,'' she recalled.

Mr. Livingston said the state public defender who took over the case after the trial challenged the effectiveness of her representation. But a number of procedural barriers at both the state and Federal level had prevented consideration of the merits of the case in the appeals process, Mr. Livingston said.

''The U.S. Supreme Court,'' he added, ''sees its job as correcting the mistakes of the state courts. But if lawyers make mistakes in presenting information to state courts, that does not get reviewed.''