The prosecution and the defense both promised jurors in opening statements that his story would back up their version of how Kent Leppink died off a Hope road in 1996.
In the end, the state's star witness delivered what prosecutors hoped he would, but at the same time he made it clear whose side he's on.
In a moment many in the crowded courtroom missed, the young man, who was a teenager when Leppink was killed, flashed a quick wink to Linehan at the defense table.
Young Carlin told the jury that the former stripper was present when his father, John Carlin III, washed a pistol in a bathroom sink full of bleach shortly after Leppink was murdered.
He also said that while he thought Leppink was "a sexual deviant," the 36-year-old commercial fisherman made no sexual advances on him.
The defense has told jurors Carlin's father, convicted of Leppink's murder, killed Leppink on his own because of sexual passes made to the younger Carlin.
Asked outside the courtroom what the wink meant, Carlin IV said it was to offer reassurance to Linehan. "She's like a sister to me," he said.
Even though he is a state witness, Carlin IV has made it clear he does not like the prosecution or investigators for the Alaska State Troopers and doesn't buy the prosecution theory of the murder. "They've gotten it wrong and manipulated what happened," he said.
He wasn't asked by either side Monday who he thinks killed Leppink, but has said in the past that he doesn't know. Leppink lived in a spare bedroom in his father's house at the time.
Carlin IV's testimony, just as in his father's trial this past spring, offered critical state evidence. It countered what defense lawyers for Linehan, now 34, claim - that Carlin III acted alone in killing Leppink to protect his son and to get Leppink out the way so he could have Linehan for himself.
New hands on gun
Carlin IV, now 28, also offered something new Monday: Earlier the same day of the gun washing, he said, he was retrieving a dog leash from a hallway closet when he found a gun in a plastic grocery bag. It fell out onto the floor; he picked it up.
Outside the courtroom, Carlin IV said he believes his father washed the pistol to get rid of his son's fingerprints.
The elder Carlin, now 50, was convicted in April of murdering Leppink. That his son handled the possible murder weapon before it got washed did not emerge at that trial. After the guilty verdict, jurors said a key reason they convicted him was because of his son's testimony.
Investigators say Leppink was killed with an uncommon .44-caliber pistol called a Desert Eagle. Prosecutors say Carlin III had a Desert Eagle but the actual murder weapon was never recovered. Lawyers for Carlin III and Linehan have never explained why they may have been washing a gun or what happened to it.
Prosecutors say Linehan manipulated Carlin into murdering her fiance so she could get a $1 million life insurance payout that she erroneously believed was coming to her.
When asked under direct examination by prosecutor Pat Gullufsen if Leppink had made sexual advances to him, Carlin IV said no.
Leppink made lewd gestures but never advances, he said. The younger Carlin testified he told his father about the gestures.
"Were you ever threatened by him with regards to being sexually molested or assaulted?" Gullufsen asked.
"No sir. Not at all," Carlin IV said.
When he was a teenager he looked up to Linehan, who then went by her maiden name Hughes, Carlin IV said. After his mother died, she was often the intermediary between him and his father, he testified. And she was also a disciplinarian. When Carlin skipped school and was acting out as a teenager, she cut the wires on his Chevy Blazer and took the distributor cap off the car to keep him from sneaking out of the South Anchorage home they all shared.
Carlin IV and Linehan left Alaska together in a motor home several weeks after Leppink was killed. He agreed he thought at the time it was abrupt. His father followed a little while later.
The Carlins maintained a friendship with Linehan over the years.
In 2005, Carlin IV stayed with Linehan at her Olympia home for several months and looked after her young daughter.
The two encountered each other Thursday on the sidewalk outside the courthouse. Despite her husband telling her not to, Linehan ran up to the young man and gave him a big hug, then left, wiping tears from her eyes.