Texas is set to execute Garcia Glen White for the murder of 16-year-old identical twin sisters on Tuesday, which would make him the sixth inmate put to death in the U.S. in a 10-day period and the fifth execution in the state so far this year.

White, who confessed to five murders in all, is set to die by lethal injection on Tuesday, 35 years after his first killing, that of 27-year-old Greta Williams in Houston.

"My sister wont be truly free until he's executed, until he pays his debt," Dewanta Washington told USA TODAY about her older sister.

White's attorneys have been arguing that his prolonged use of crack cocaine, in combination with a number of head injuries over the years, are what drove him to violence and that he doesn't deserve to die. Those who knew him before the drugs describe White as a gentle giant whose life went off the rails because of football injuries, job loss and an ensuing drug addiction.

"Glen was the kindest person I knew," a friend named Ray Manuel wrote about White, according to court records obtained by USA TODAY.

Here's what you need to know about the execution.

Who is Garcia Glen White?

White, 61, was a star football player who grew up in a loving home with his six siblings. An injury derailed his sports career in his first year at Lubbock Christian College and his girlfriend got pregnant, so he dropped out and started working to support his new family, according to court records.

White eventually had two more children and was working fulltime when another injury cost him his job. Soon after that, White turned to the comfort of drugs, and crack cocaine later took over his life, court records say.

"He didn't have any structure in his life," a friend named Howard Gordon said in court records. "I could see him changing, and when I saw the guys he was hanging out with, I knew that no good would come of it."

After White's crimes became known, Gordon said he couldn't believe it. "Until he got hooked on the drugs, there was nothing in him that would have ever done this."

Before the drugs, White's family described him as a meek man who wouldn't harm anyone. His younger sister, Monica Garrett, said that "Glen was quick to cry," court records say. And his older brother, Alfred White Jr. said: "He was the biggest wimp you'd ever find."

What was Garcia Glen White convicted of?

In all, White confessed to killing five people in three separate attacks. The first was Greta Williams, a 27-year-old who was beaten to death in 1989 just a few months after she moved to Houston from Chicago for a fresh start. A couple months later, White killed a Houston mother named Bonita Edwards and her identical twin daughters, Annette and Bernette Edwards, just one day after their 16th birthday and a few weeks before Christmas in 1989.

The Edwards' bodies were riddled with stab wounds in various states of undress, and strong evidence showed that Bernette had been sexually assaulted, court records show. Their murders went unsolved for six years.

And then, in 1995, White beat to death a convenience store worker and father of seven named Hai Pham.

White was being held in Pham's murder when one of White's close friends told police that White had admitted killing the Edwards family. On top of White's eventual confession, his DNA was a 99.9999% match to semen found on Bernette.

The ensuing investigation found that White and Bonita Edwards had been using crack cocaine while her daughters were in their bedroom. White told police that he and Edwards began fighting,

"She reached for a knife, and I took the knife and stabbed her," he said, according to court records. "Some kids come out. I went into the bedroom after them. ... I stabbed one in the bedroom and one in the living room."

Off all the murders, prosecutors only pursued charges in the Edwards case, and White was found guilty of murdering Annette and Bernette.

Who were Garcia Glen White's victims?

Dewanta Washington told USA TODAY that her sister, Greta Williams, was beaten so "beyond recognition" that the family couldn't have an open casket.

Washington said that she and Williams were just two years apart, growing up as best friends who did everything together and dreamed of one day getting married and having children. Williams never got the chance before her murder.

Washington said she's planning on traveling back to where her family is from in Chicago to finally spread her sister's ashes and let her rest.

Not much is known about Bonita Edwards and her identical twin daughters, Annette and Bernette. But the day before they were all killed, the girls had turned 16 and begged their grandmother to let them come live with her, Harris County prosecutor Josh Reiss told USA TODAY.

"Two dead 16-year-old girls kind of speak for themselves in terms of the savageness of these crimes," he said.

The fifth victim, Hai Pham, had moved his wife and his four youngest children to the U.S. in September 1994. Nine months later, White killed him in the middle of the day in the convenience store where he worked while his 14-year-old son napped nearby, according to one of Pham's other sons, Hiep Pham.

Hiep Pham, who was 17 at the time of the murder, told USA TODAY that his father had been teaching his children English even before they left Vietnam, and that his big dream was for his other grown children to eventually reunite with the family in the U.S. − a dream that never came true.

As Hiep Pham grew up in Houston without his dad, struggling to learn English, dropping out of school to work two jobs and help put food on the table, he said he eventually realized how big of a deal Father's Day is here. It made him miss his own dad that much more.

"I feel angry still," said Pham, fighting tears. "We never celebrated Father's Day for my dad. And I always dreamed of that, having a beer with my dad."

When will Garcia Glen White be executed?

White is set to be executed just after 6 p.m. CT on Tuesday, Oct. 1, at the Texas State Penitentiary in Huntsville, just north of Houston.

Who is witnessing the execution?

Both Washington and Hiep Pham told USA TODAY that they will witness the execution. Both of them are looking for closure on Tuesday.

"He has lived longer in prison than my sister lived on this Earth," Washington said. "It's time for him to pay the piper. He just needs to go meet his maker."

Pham said that he felt relief when he learned that White's execution had been scheduled.

"I went back home and told my family during dinner that night: 'I don't know about y'all, but I'm going,'" he said. "It's hard to see somebody die, but I think it's justice for my dad."

When is the nation's next execution?

Two inmates are scheduled for execution on Oct. 17.

Texas is set to execute Robert Leslie Roberson despite what the Innocence Project says is "new evidence that he is an innocent man wrongly convicted under the now-debunked shaken baby syndrome (SBS) hypothesis." Roberson was convicted in the 2002 death of his 2-year-old daughter Nikki.

At virtually the same time as Roberson's execution, Alabama is set to execute Derrick Ryan Dearman in the killing of five people, including a pregnant woman, in 2016.

White is the 19th inmate to be executed in the U.S. this year, and Roberson and Dearman will become the 20th and 21st.