CARROLL, IOWA - His fate in the hands of a jury, Michael Swanson was escorted past a group of TV cameras Thursday in the Carroll County Courthouse. The 18-year-old extended both middle fingers and smiled.

That was before he learned he would spend the rest of his life in prison for shooting convenience store clerk Sheila Myers in the face, killing her. That, too, didn't seem to faze him.

"I'm good," he said with a grin following his convictions for first-degree murder and first-degree robbery.

It took a jury less than an hour to convict Swanson for Myers' slaying on Nov. 15, 2010, rejecting defense attorney Charles Kenville's argument that the defendant, then 17, was insane and didn't know right from wrong when he shot and killed her.

Swanson gave a grin and swiveled in his chair when the verdict was read. Myers' husband of 37 years, Roger, and daughters Mandy and Robin showed little reaction, as they have throughout the trial.

A first-degree murder conviction in Iowa carries an automatic sentence of life without parole. But formal sentencing will be scheduled after Swanson's trial next month in Rock Rapids, Iowa, for allegedly shooting and killing clerk Vicky Bowman-Hall, 42, in Algona, Iowa, the same night.

The remarkably fast verdict followed a speedy four-day trial in which Assistant Iowa Attorney General Becky Goettsch presented several pieces of evidence.

The most compelling was a two-hour videotaped interview with Iowa investigators, in which Swanson calmly discussed stealing his mother's Jeep and credit cards, heading north to a family cabin in Bigfork, Minn., and then south to Humboldt, Iowa. That was where he robbed Myers, 61, at gunpoint for $31 before shooting her and walking out of the store. She died behind the counter.

Myers' relatives told reporters they weren't surprised by the quick verdict. The trial was difficult for them, especially when photos were shown of Myers' body. They stayed, they said, because they believed they owed it to their wife and mother.

"We wanted to be here for her," Mandy Myers said. "We didn't want it to be all about him."

'Happy as a clam'

Attention after the crimes had focused on Swanson, who laughed and smiled at reporters as he was walked to his first court appearance last fall.

During the trial, testimony centered on the evidence and Swanson. The courtroom was riveted by the video of Swanson, smoking cigarettes and sipping a soda, flatly describing the crime to an Iowa investigator. He smiled and scratched his head when he described the gasping sound Myers made when he shot her.

Swanson showed little reaction to much of the testimony, including two hours on the stand by his mother, Kathleen Swanson, the defense's lone witness. She related 18 years of attempts to get help for her son and said she often lived in fear of him.

She broke down sobbing when psychiatrist Michael Taylor, who said he believed Swanson was not mentally ill, testified Thursday morning that the teenager told him he had planned since age 13 to go on a spree of "murder, rape and cannibalism" with his parents as the first victims.

"He's happy as a clam. He's killed somebody," said Taylor, a rebuttal witness for the prosecution. "He's getting all this attention. We're all here. It's a dream come true."

Remorse, Taylor said on the stand, was beyond Swanson's comprehension.

"In Mr. Swanson's perspective, people are going to die. What difference does it make when they die when they're 77 or when he shoots them?" Taylor said. "He could not understand why everybody was getting so upset about this whole situation."

'It'll never be over'

When the jury notified court officials and family members that it had reached a verdict about an hour after they started deliberating, Kathleen Swanson trudged into the courtroom sobbing. She and her husband, Robert, had just released a statement expressing sympathy to the Myers family and pledging to stand by the son they said they loved despite years of failed attempts to get him help.

"We are heartbroken by these events," they said in the statement. "We hope the trial will present the desperate realities some families face whose children suffer from mental illness."

Roger Myers said he thought Kathleen Swanson's testimony was "put on," although Mandy Myers said she understood she was trying to help her son.

During closing arguments, Goettsch used nearly every step Swanson took to prove he knew exactly what he was doing. Any suggestion that he didn't, she said, "is ridiculous on its face."

Kenville pressed the jury not to rely on emotion but rather on the facts, which he said indicated "the lights are on but nobody's home. He just has no clue about how wrong his acts are."

Kenville and Goettsch left the courthouse without commenting, as did several jurors. One, who did not give his name, explained the fast verdict: "I think the facts took care of themselves."