As his attorneys stuck to his self-defense account, a 19-year-old from Mount Pleasant who typed text messages about murder before slicing a schoolmate to death was sentenced Wednesday to 18 years in prison for what some called a ruthless crime.

Matthew Fischer was 16 when he stabbed 17-year-old Lucas Cavanaugh during a feud over Fischer's girlfriend in the town's Park West neighborhood.

Though Fischer argued he was trying to get out of Cavanaugh’s grasp during a mutual fight — a story that had already failed to prompt a dismissal of his murder charge — prosecutors cited messages in which he talked about killing Cavanaugh a week before the Jan. 18, 2015 slaying.

Avoiding a trial, he pleaded guilty earlier this month to a lesser count of voluntary manslaughter, which carries between two and 30 years behind bars.

During a tearful two-hour sentencing hearing in a packed Charleston courtroom, Circuit Judge Markley Dennis noted Fischer’s youth and mental health struggles at the time of the killing. He said Fischer would need continued help during and after the prison sentence to ensure he “doesn’t slip back into the person he was.”

“It wasn't self-defense," Dennis said. "He didn't need to do it."

Under state law, Fischer must served 85 percent, or about 15 years, of the total prison term.

Moments before learning his fate, the young defendant turned briefly to dozens of Cavanaugh’s loved ones who had described a widely loved young man who aspired to design cars and start his own business.

Fischer apologized. His father Joey and mother Susan had done the same.

Matthew Fischer Sentencing

Matthew Fischer (center) sits with his family before being sentenced Wednesday to 18 years in prison for the 2015 deadly stabbing of 17-year-old Lucas Cavanaugh. Brad Nettles/Staff

“I regret it every day,” he said. “I don’t know what I can say. I’m just really sorry.”

Members of Cavanaugh's family had asked for Fischer to be imprisoned for the maximum term.

"Whatever happens," his father, Dave Cavanaugh, said, "there will be no justice for Luke. Luke is still dead."

The three teens involved in the deadly confrontation knew each other from Wando High School.

Fischer was visiting his girlfriend on Baltusrol Lane when she got text messages from Cavanaugh. She would later tell police the texts were sent through Snapchat, a service whose messages disappear after a time. The account proved wrong, and investigators from the Mount Pleasant Police Department found the Apple iPod messages.

Fischer grew angry and jealous, but Cavanaugh insisted that he wouldn’t steal the girlfriend.

"I'll ... kill you,” Fischer texted, taking over the conversation. “Come here right now."

Cavanaugh drove from Sullivan's Island to Mount Pleasant.

Defense attorneys continued Wednesday to portray Cavanaugh as the aggressor who charged after Fischer once he arrived.

They fought.

One of Fischer’s lawyers, Peter Brown, said Cavanaugh wrapped Fischer in a headlock. That’s when Fischer pulled out a pocketknife that his girlfriend had given him and sliced at Cavanaugh’s arm, Brown said. Cuts on the sleeve of Cavanaugh’s sweater supported the account, the lawyer said.

The last, fatal blow was a stab to Cavanaugh’s gut. His last sight, his loved ones said, was likely of his own gruesome injury.

Lead defense attorney Andy Savage said Fischer should have kicked and flailed to suppress the “threat” he saw in Cavanaugh.

But he “used a knife in self-defense,” Savage said, “when a knife was not appropriate.”

Prosecutors said earlier text messages expressing thoughts of violence and ill will against Cavanaugh showed that he had carried out malicious intentions that had been brewing for some time.

“Obviously, he had a dark and disturbed side,” Assistant Solicitor Jennifer Shealy said at the sentencing. “He thought of murdering people.”

For more than an hour, Cavanaugh’s supporters describing losing an old soul who had friends young and old, gay and straight, black and white — a remarkable diversity for someone his age. He fixed cars by watching YouTube videos and wanted to earn a college degree in automotive design.

Matthew Fischer Sentencing

Beth Cavanaugh, mother of Lucas Cavanaugh, speaks before Matthew Fischer was sentenced Wednesday to 18 years in prison for the 2015 deadly stabbing of her son, Lucas Cavanaugh, 17. Brad Nettles/Staff

His friends and family miss his dinosaur sounds, his mischievous sense of humor.

One friend turned to drugs to cope with the loss.

His youngest brother, Dirk, still sleeps on Cavanaugh’s bedroom floor.

“He’s irreplaceable,” the brother said.

To remember him, they made quilts of his shirts.

“We have cried years' worth of tears,” his mother, Beth Cavanaugh, said. “To say our lives will never be the same is an understatement.”

Cavanaugh would have turned 20 years old on Thanksgiving. His father looked around that day, thankful for the family, including two other sons, he still has.

“There’s nothing like having something ripped away from you to make you appreciative for what you have,” he said. "But there’s a huge undercurrent of melancholy and despair.”

And that, loved ones said, will never go away.

Reach Andrew Knapp at 843-937-5414. Follow him on Twitter @offlede.

Andrew Knapp is editor of the Quick Response Team, which covers crime, courts and breaking news. He previously worked as a reporter and copy editor at Florida Today, Newsday and Bangor (Maine) Daily News. He enjoys golf, weather and fatherhood.