NEW BOSTON, Tex. — Scottie Forcey nervously drummed his fingers behind the thick glass in the Telford Unit’s visiting room as the camera shutter snapped, capturing images of the 21-year-old convicted murderer.

“I want some pictures. I ain’t seen myself in like” — he paused to count on his fingers — “five years. I know I look different. Check it out.” He pressed his prison ID card against the glass. In the photo, a plumper, baby-faced 17-year-old stared at the camera.

Mr. Forcey was convicted in 2009 of fatally shooting Karen Burke, a 52-year-old Alvarado convenience store clerk. He is the youngest of 23 Texas Department of Criminal Justice inmates who received mandatory sentences of life without parole for committing capital murder when they were younger than 18.

Now, as legislators work to comply with a United States Supreme Court ruling, those inmates could become eligible for parole after serving 40 years.

The justices ruled last year that sentences of life without parole for 17-year-old murderers violated the constitutional ban on cruel and unusual punishment. Either the courts or Gov. Rick Perry could change such sentences in Texas. But both are waiting for legislators to decide what punishment juveniles like Mr. Forcey should face. Lawmakers, who failed to pass legislation in two sessions this year, are trying now for a third time.

In Texas, 17-year-olds have faced the same sentencing options as adults convicted of capital murder: the death penalty or life without parole. In 2005, the Supreme Court prohibited the death penalty for anyone under 18, deciding that the less-developed brains of juveniles rendered them less culpable. That left only life without parole as the punishment for 17-year-olds.

After the court’s decision last year, in Miller v. Alabama, prosecutors said they had no sentencing options for 17-year-old killers. They asked lawmakers to make them subject to the same punishment Texas law requires for 14- to 16-year-old capital murderers: life with parole eligibility after 40 years.

Lance Long, a Harris County assistant district attorney, recently told lawmakers that until they decided on a sentencing option, such murder trials were being delayed across Texas.

“None of these cases are anything but very, very, very serious,” Mr. Long said.

The Texas Senate’s Criminal Justice Committee has approved a bill that would require a sentence of life with parole eligibility after 40 years. The House, however, has indicated it wants to give juries the option to sentence 17-year-olds to life without parole if other factors — like evidence of abuse or mental illness — are considered.

In previous sessions this year, both chambers approved bills addressing the sentencing question, but time ran out before they could get final approval.

Mr. Perry has told prosecutors that when lawmakers decided on a new sentencing bill, he would consider recommending commutation for inmates like Mr. Forcey who were sentenced under the old law.

“It really only seems fair and just,” said Justin Wood, the legislative liaison for the Harris County district attorney’s office in Houston.

Mr. Forcey, meanwhile, contends that he did not pull the trigger in Ms. Burke’s murder in 2008. He said he was targeted because he ran with the wrong crowd.

Now, he said, “I wouldn’t put myself in that situation.”

Mr. Forcey has spent most of the last four years in isolation, punishment for fights he said were constant when he first arrived.

“I grew up back there,” he said.

Asked about the possibility that his sentence could be commuted, Mr. Forcey was ambivalent. Forty years, he said, is too long.

Then a wide smile spread across his face. He figures he will be out by December. Mr. Forcey spent those years in isolation researching his case, he said, and plans to file an appeal.

“My mind’s already set,” he said. “I’m going home — wherever home is.”