Connecticut carried out its first execution in 45 years early Friday, administering a lethal injection to Michael Bruce Ross, a convicted serial killer who abandoned his appeals and died willingly after 18 years on death row.

Death penalty opponents held vigil outside the rural complex of state prisons where a warden led Mr. Ross to the execution chamber and an unidentified executioner administered a lethal injection into his arm at 2:13 a.m. He was declared dead at 2:25 a.m.

Mr. Ross, 45, had sought that fatal moment for nearly a year.

In defiance of public defenders and others who wanted to save him, he chose to forgo further appeals of his death sentence last year. He said he wanted to ease the pain of the families of the eight teenage girls and young women he strangled in the early 1980s. He raped most of his victims.

A graduate of Cornell University and a former life insurance salesman, Mr. Ross convinced judges he was competent, smirked at psychiatrists who said he was suicidal and often seemed exasperated by his inability to reshape his image.

"I am not an animal," he once wrote.

Late Thursday, the United States Supreme Court rejected two efforts by others to block the execution. Yet because of his status as a so-called volunteer, Mr. Ross had the right to change his mind up until the moment of the lethal injection and to say he wanted to appeal.

"All he has to do is say so, and the machinery of death will stop," Attorney General Richard Blumenthal said during a news conference at a prison just down the street from the prison where Mr. Ross was to die.

The execution had seemed imminent before. In January, Mr. Ross came within hours of death before his lawyer, T. R. Paulding, unexpectedly requested a delay. Mr. Paulding, who has helped Mr. Ross seek execution, cited a potential conflict of interest after a federal judge threatened earlier that day to suspend his law license for not questioning Mr. Ross's competency more thoroughly.

A new six-day evaluation in April led to another finding of competency and a series of court rulings affirming the finding. One expert said this week that he believed that the execution would go forward because the state effectively has had a legal "dress rehearsal."

"I think last time cleared a lot of the underbrush out of the way," said the expert, Michael A. Mello, a professor at Vermont Law School and a former capital defense lawyer.

By late Thursday, some families of Mr. Ross's victims were preparing to watch him die at the Osborn Correctional Institution, atop a grassy slope less than a mile from the Massachusetts border. Family members would share a viewing room with four people there to support Mr. Ross and five news media witnesses allowed to document the event with notepads and pens. Curtains would separate each group.

Lan Manh Tu, whose younger sister Dzung Ngoc Tu, 25, was raped and murdered by Mr. Ross in 1981, was traveling to Connecticut from Maryland on Thursday for the execution. Mr. Ross was never prosecuted for her murder, though he confessed to it. Mr. Tu did not plan to witness the execution, but would be nearby.

"I'd like to be somewhere in the vicinity because I feel an obligation to my little sister and my family," he said.

On the rural two-lane road that runs past the prison complex here, drivers beeped horns or shouted support or disapproval as they passed clusters of correction officers and state police officers. About 100 people gathered at Somers Congregational Church nearby about 10 p.m. to pray and to listen to speakers before marching to the prison.

"I'm not here because of Mr. Ross," said David Cruz-Uribe, 41, who teaches math at Trinity College in Hartford. "He's not a nice person. I'm here because I oppose the death penalty."

Lawyers argued in court as late as Thursday afternoon. A motion filed by one of Mr. Ross's sisters claimed his decision to be executed was involuntary because he suffered from a combination of mental disorders and psychological coercion after years of confinement. Another suit claimed that Mr. Ross's "suicide" would "cause suicide contagion" among other inmates. Both claims were rejected late in the day.

Mr. Ross's unlikely case pushed Connecticut toward its 74th execution since it adopted capital punishment in 1893. But it would be the first since the state electrocuted a murderer named Joseph Taborsky in 1960.

On Thursday morning, Mr. Ross woke at 5:45 and "spent part of the morning watching television, reading newspapers," said Brian Garnett, a spokesman for the State Department of Correction.

By 8:10 a.m. he was moved to a holding cell next to what correction officials call "the execution enclosure." He took with him a Bible, a book of Bible verses, a coffee cup and candy. He received communion from a prison chaplain about 9 a.m. and received visits from his lawyer, friends and family, speaking to them through holes in plexiglass.

About 3 p.m., he was served the last prison meal of the day. "That happened to be turkey a la king with rice, mixed vegetables, white bread, fruit and a beverage," Mr. Garnett said.

Julia Preston, in Manhattan, and Avi Salzman, in Somers, Conn., contributed reporting for this article.