Dr. George Corvin testified Monday for the defense during the sentencing phase of the trial. Hembree, 49, was convicted last week in the death of 17-year-old Heather Catterton.
Catterton died in October 2009 after a night of smoking crack and having sex with Hembree.
Hembree's attorneys, Rick Beam and Brent Ratchford, aimed to prove that Catterton died of an overdose. Jurors instead went with the scenario Hembree mapped out in police interrogations in which he confessed to suffocating the teenager.
He later recanted those confessions from the witness stand.
Hembree has spent nearly 20 years of his life in prison.
According to Corvin, Hembree's disorders are better controlled when he's incarcerated.
"Prison is actually a pretty good management system for people with personality disorders," Corvin testified.
Outside of constant care, Hembree engages in destructive behavior, Corvin said.
Hembree's illness has prompted him to cut and burn himself, overdose on drugs and alcohol and intentionally drive a car into a tree in a suicide attempt, the doctor testified.
None of those behaviors surprised Corvin, who reviewed Hembree's case prior to the trial.
Corvin said Hembree's addictions only exasperate his already sensitive mental state.
"It's like throwing fuel on the fire. It's going to make it far worse," Corvin said of Hembree's condition.
Hembree has struggled with cocaine addiction for years, according to testimony from his friends.
Prison life offers Hembree a forced sobriety that can keep his condition in check, Corvin said.
But Gaston County District Attorney Locke Bell disagreed.
Bell asked the doctor about the 10 times Hembree had been written up for bad behavior in prison. One such time included an assault on an officer, Bell said.
According to Bell, Hembree attacked a detention officer, hopped over two fences, then stole a vehicle to escape from prison.
Corvin said the majority of Hembree's infractions in prison were non-violent.
Hembree was born the oldest of four children. His mother was 18 at the time. His father was a strict military man.
The stern father figure often drank vodka, became violent and took it out on his son, according to testimony by Hembree's cousin, Robin Collier.
Collier said he and Hembree were like brothers. He testified that the two partied together, and that Hembree's father didn't react well when he learned his son wasn't behaving.
"He beat the s - - - out of him," Collier said more than once from the witness stand.
Hembree's father would use his hand, a belt or a switch to discipline both his sons, according to Collier.
And both sons suffered from mental illness, Jacqueline Hembree testified Monday afternoon.
Danny Hembree often helped out with caring for his siblings, according to his mother's testimony.
"You couldn't ask for a better child as far as loving and caring, until he became a teenager and started having these problems," she said.
Danny Hembree seemed to be a nervous child, according to his mother. He started chewing the skin around his finger nails and started disrupting class.
His parents took him to a pediatrician, where he was diagnosed with depression.
Hembree attended Hunter Huss High School but dropped out before graduation.
He got married at 18 and started a family with a 16-year-old neighbor. He was already in trouble, according to his ex-wife who testified Monday.
"He was already addicted to drugs," said Mary Shidagis.
Shidagis talked about how Hembree's demeanor would change depending on whether he was using cocaine. Under the influence, he was a different person, she said. He hit her, Shidagis testified.
The couple divorced after 14 years of marriage.
For the second time in less than a week Hembree's attorneys attempted to have the guilty verdict set aside.
Defense attorneys Brent Ratchford and Rick Beam made a motion Monday morning to throw out the verdict. The basis for the motion was that some jurors could've been influenced by members of Catterton's family while taking smoke breaks.
Superior Court Judge Beverly Beal called five jurors into the jury box individually. He asked each of the five smokers if they had been approached by anyone involved in the case while taking smoke breaks. Each said they had not had any such encounters, and Beal in turn denied the motion.
Wednesday, Hembree stood before Beal and expressed dissatisfaction with how his trial was conducted. He said his attorneys had not provided him with all of the evidence, and he considered himself to be an active participant in his trial.
Hembree made a motion to have the verdict thrown out because of inadequate representation.
Gaston County District Attorney Locke Bell objected to the motion, stating that Beam and Ratchford gave the prosecution a run for their money in the lengthy trial.
Beal denied the motion, and the sentencing phase of the trial began.
Jurors are listening to evidence for the defense before deciding if Hembree should be put to death or sentenced to life in prison.
The prosecution offered up witnesses last week in an effort to show a pattern of violent behavior.
Hembree has a lengthy criminal record including a string of armed robberies in Mecklenburg County shortly before he was charged with Catterton's killing.
If jurors agree that Hembree is a violent felon who could be a danger to himself or others, they could sentence him to death.
The defense began calling its witnesses Monday in an attempt to prove that he can be a productive person in prison.
The defense expects to call its final witnesses Tuesday. Beal predicted that closing arguments would take place Wednesday.