— -- The mother of Conrad Roy, a Massachusetts teenager who died of carbon monoxide poisoning after locking himself in his truck following encouragement from his then-girlfriend, Michelle Carter, says, "My pain will always be the same."
"I wake up each and every day with pain and heartache living without Conrad," Roy's mother, Lynn Roy, said in an exclusive statement to ABC News' "20/20." "The same pain I felt the day Conrad died. Regardless of what happens to or where Michelle Carter is, my pain will always be the same."
Conrad Roy was 18 when he died in July 2014 after locking himself in his truck. On Thursday, Carter was sentenced to 2.5 years after she was convicted of involuntary manslaughter in Roy's death earlier this year.
"He was the most selfless giving person I have ever met," Lynn Roy said in the statement. "He was humble and always strived to help others."
She said she hopes a new law called "Conrad's Law" can allow "his legacy to live on."
She did not elaborate on what she hopes the law would be, but said in the statement, "I want to counter all of the negativity Michelle has brought to this world with some of Conrad's positivity."
When Carter, who was 17 years old and Conrad Roy's girlfriend at the time of his death, went on trial this summer, the prosecution argued that she was reckless and caused his death by telling him to get back in the gas-filled car even though prosecutors said he didn’t want to die.
"I could’ve stopped him," Carter texted a classmate two months after Conrad Roy's death, according to testimony. Carter texted that she and Conrad Roy were on the phone at the time of his suicide when he "got out of the car ... he was scared." Carter texted that she "told him to get back in."
Prosecutor Katie Rayburn told "20/20," "What we know from the text messages is that she was trying to manipulate him and she wanted him to die. ... This was calculated. "
Prosecutor Maryclare Flynn told "20/20" that Carter "used him as a pawn in her sick game."
"These friends that she had thought that she had and developed over the school year were now going off and doing their own thing, getting ready for college, working, and she was losing that attention, and so she needed something," Flynn said.
Carter did a "dry run," Flynn explained, "telling her friends that he was dead two days before he was even in that truck," and she's getting "the attention that she so thinks that she deserves. And so afterward, when she has told them that he’s missing and maybe dead, she has to make it happen."
Carter's defense attorney, Joseph Cataldo, told "20/20," "Michelle didn’t come into this relationship anything but a young girl struggling with her own mental health issues, until Conrad Roy prodded her into his suicidal thinking. Michelle was not thinking Conrad should ever kill himself.
"It was Conrad Roy laying a lot of his baggage on Michelle Carter," he said. "The two years that they were texting... he consistently bombarded her with his suicidal thinking."
"I think over the course of the two-year texting relationship he wore her down," Cataldo said. "She came to realize that Conrad was going to kill himself, no matter what, and so she felt that she should help him and encourage him to do what he wanted to do. ... That’s the tragedy here, that she thought she was helping him achieve his goal.
"He put in so much time and research into searching on the internet how to take his own life," Cataldo said. "She didn’t manipulate him, she wasn’t in his house when he was researching all the various ways to kill himself."
The day of Conrad Roy's death, "He chose to step back in that truck and end his own life. It was his decision," Cataldo said. "He did not hang up the phone, he did not call 911."
Carter was sentenced Thursday to 2.5 years in the county House of Correction with 15 months to be served and the rest suspended, followed by five years of probation. In announcing Carter's sentencing, Judge Lawrence Moniz said that she could stay free pending appeals.
Cataldo said today that while "we were hoping that she would get probation, that she would receive no jail sentence whatsoever," Carter is remorseful and "very relieved" to stay free at this time.
The prosecution had asked the judge to sentence Carter to seven to 12 years in prison. Flynn said today, "We wished that the judge had recognized that Conrad’s life was worth more than 15 months in the House of Correction.
"It was our hope and belief that she would be taken into custody," Flynn added, "and we were very upset and we certainly felt the family’s outrage that she walked out when they didn’t have their son."
Flynn added, "She still is, we believe, going to serve jail time. Justice will be done. It has been done with the verdict. ... It will just take a little bit of time."
Meanwhile, Cataldo said he is "confident that eventually the appellate courts will see Conrad Roy's death for what he says it is: a tragedy and not a crime. "I’m very optimistic that it will eventually be overturned on appeal," he said.
Rayburn said she thinks a takeaway from this case is that "words have meaning."
"Some people think that I can just text or write online whatever I want and it doesn’t matter -- and it does," she said.
Regarding the Roy family, Flynn said, "The verdict doesn’t end their tragedy but at least it gives them some sense that their son’s life mattered and they know that he was a homicide victim. ... And I know that Lynn and all the members of the Roy family are looking to pursue any type of legislation so that would make another family not go through the pain and suffering that they have gone through."
Watch the full story on ABC News' "20/20" TONIGHT at 10 p.m. ET
ABC News' Joseph Diaz contributed to this report.