The second of four men to plead guilty for their roles in a slaying aboard a boat at a Mystic marina in September 2008 was sentenced on Monday during a court appearance in which all sides lamented the tragedy of unintended consequences.

Vincent Green, 19, was sentenced to 25 years in prison after accepting a plea agreement under the Alford Doctrine, which means he doesn't agree with the state's allegations but does not want to risk conviction and the possibility of a lengthier sentence at trial.

His sentence is the mandatory minimum sentence for felony murder.

Green and Christopher Allen, 24, formerly of Mystic, boarded the boat Crucible on Sept. 26, 2008, with the intention of robbing 29-year-old Kyle Sheets of money and drugs, according to prosecutors. A struggle ensued and Allen stabbed Sheets multiple times.

Two other men, Bryan Sutton and Bruce Grisafe, served as lookouts during the botched robbery and are awaiting sentencing.

Sutton, 19, pleaded guilty last Thursday to serving as a lookout on the dock at Seaport Marina. He will be sentenced June 24 to up to six years in prison for accessory to first-degree robbery.

Grisafe is scheduled to be sentenced to up to six years in prison on May 28.

Green, who appeared on the verge of tears for most of the sentencing Monday, apologized when asked if he wanted to address the court.

"I'm sorry," he said. "I didn't expect what happened to happen. If I could take it back, I would, but I can't. I think about it all the time. … I know I can't be forgiven and it can't be forgotten. All I can say is I'm truly sorry."

Judge Susan Handy, who during Allen's sentencing had said the case represents "an exponential factor of stupidity," said she had asked herself what motivated the four young men that day. Were they bored, she wondered, and then thought, "Let's go rob somebody"?

"Where I come from, that's just bizarre," Handy said. "That's just bizarre. … Out of what appears was boredom, you came up with this ridiculous scheme. Now you've been sitting in jail since 2008."

Prosecutor Lawrence Tytla pointed out that any one of the four could have stopped things.

"All it would have taken is for one of them to say 'That's dumb, that's stupid, that's asinine,' " Tytla said during the sentencing in New London Superior Court.

None of the four expected a murder to occur, Tytla acknowledged.

"But the way the law handles it (is), when you intend to commit a serious crime and something much, much worse happens, you're responsible for that," he said.

Sheets' father, Russ, criticized the Alford Doctrine before the sentence was imposed and again outside the courtroom.

"The Alford Doctrine allows Mr. Green to spend the sentence without admitting any guilt," he told the court. "And I think that's a tragedy."

"That's an injustice to you," he said to Green.

"To spend those years in prison, thinking that you were innocent, I can't imagine the resentment that must be felt by you," Sheets said. "And that is going to do you no good."

Green's mother, Brenda Langley, said afterward that 25 years was too long a sentence. She questioned why Allen, who committed the crime, got just seven more years for the actual murder.

"I'm his mom and I'm not saying he should walk," she said, "but that's uncalled for. … I'm not saying my son's innocent, but he shouldn't have gotten 25 years."