HARTFORD — Kennedy cousin Michael Skakel's conviction for a 1975 murder was the result of a myriad of poor decisions by his trial lawyer, who failed to tell jurors that his brother might have committed the killing, Skakel's appellate attorney told the Connecticut Supreme Court on Wednesday.

Outside the courtroom, Skakel's cousin Robert F. Kennedy Jr. repeated previous statements he has made about evidence showing two other men killed teenager Martha Moxley, who was bludgeoned to death with a golf club in the wealthy Greenwich neighborhood where she and the Skakel family lived at the time.

Prosecutors went before the state's highest court Wednesday to argue that Skakel's 2002 murder conviction should be reinstated.

Skakel, 55, a nephew of Robert F. Kennedy's widow, Ethel, had been sentenced to 20 years to life in prison. But a judge in 2013 ordered a new trial after finding that defense attorney Michael Sherman failed to adequately represent his client.

Skakel, now free on $1.2 million bail, sat next to Kennedy Jr. in the gallery of the courtroom during the arguments. Skakel declined to comment.

It's not clear when the court will issue its decision.

Prosecutor Susann Gill told the justices that Sherman, who has defended his work, did a competent job investigating and trying the case, and that Skakel's appellate lawyers have not met the high burden under case law to prove ineffective counsel. She also stood by the state's position that there was "substantial" evidence that Michael Skakel killed Martha Moxley.

Gill noted that Sherman put together a defense team that included other lawyers and several investigators.

"This was far from a slipshod defense," Gill said. "This was a well-planned ... well-thought-out defense. Mr. Sherman pulled in a lot of resources and presented a coherent defense."

Hubert Santos, Skakel's appellate lawyer, said Sherman made numerous poor decisions, including not focusing on Skakel's older brother, Thomas Skakel, as a possible suspect.

"This defendant did not get a fair shake," Santos told the court. "The weight of the evidence is that Tommy Skakel killed Martha Moxley."

Santos also said Michael Skakel had an alibi on the night of the killing at 10 p.m., the time that he said evidence shows Moxley was killed. He cited testimony that Michael Skakel and some relatives left the neighborhood at about 9:30 p.m. to go to his cousin's house 20 minutes away to watch a Monty Python movie.

Santos accused prosecutors of moving the time of the killing to an undetermined time between 9:30 p.m. on Oct. 30, 1975, and 5:30 a.m. the next day, in response to Skakel's alibi. Prosecutors deny that.

Santos also said there was no forensic or physical evidence linking Michael Skakel to the killing.

Thomas Skakel's attorney has previously said that his client had nothing to do with the slaying.

Thomas Skakel was an early suspect in the case, because he was the last person seen with Moxley. Santos said Thomas Skakel admitted to investigators hired by his father that he had a sexual encounter with Moxley in which he unbuttoned her jeans and pulled them down between 9:30 and 9:55 p.m. on the night of the killing. Moxley was found dead the next day with her pants pulled down.

But prosecutors have said that highlighting Thomas Skakel's relationship with Moxley actually would have bolstered their argument that Michael Skakel killed her in a jealous rage.

Michael Skakel, who like Moxley was 15 years old at the time of the killing, had admitted to two women that he was aware his brother had sexual contact with Moxley the night of the murder and told one woman that is what triggered it, prosecutors wrote in court documents. But prosecutors say the trial defense rightly decided not to focus on Thomas Skakel because there wasn't sufficient evidence.

After the hearing, Moxley's mother, Dorthy Moxley, 83, said the appeal process has been frustrating.

"I'll just be glad when it's over," she said. "I want him back in jail."