"He had some very, very, very serious issues," attorney Allen Bickart tells PEOPLE

Arizona criminal defense attorney Allen Bickart has defended many people during his 60 years of practicing law, but last week, the case of one client came back to haunt him.

“He was a very troubled, very vicious kid,” Bickart tells PEOPLE exclusively, describing his brush with Todd Kohlhepp, a South Carolina man who police have linked to seven murders. Bickert represented Kohlhepp back in 1987, after he was arrested for allegedly raping a 14-year-old neighbor at gunpoint in Tempe, Arizona, at the age of 15, according to court records obtained by PEOPLE.

Kohlhepp ultimately pleaded guilty to kidnapping, served prison time from 1987 to 2001, and was placed on the sex offender registry, according to records.

“That girl should be very lucky he didn’t kill her,” recalls Bickart, 85.

Kohlhepp emerged in the news on Nov. 3 when police, acting on a tip, arrived at the 45-year-old real estate agent’s 95-acre property in Woodruff, South Carolina, and discovered a woman inside a metal storage container. According to the local sheriff, she had been “chained up like a dog” for the past two months.

The body of her boyfriend, who had reportedly been shot to death, was found buried nearby in a shallow grave. Two additional bodies were also discovered buried on the property, revealed Wednesday to be married couple Meagan Coxie, 25, and Johnny Coxie, 29, police tell PEOPLE.

When questioned by police two days later, Kohlhepp confessed to the unsolved murders of four people at a motorcycle shop in 2003. He has so far only been charged in the 2003 murders.

“He had some very, very, very serious issues,” says Bickart, who worked with a psychiatrist in an effort to get his client sent to a facility where mental health specialists could attempt to help the violence-prone teen — instead of prison. “He was off the edge.”

Kohlhepp “took responsibility for what he did,” adds Bickart, but soon his case was bumped from juvenile to adult court, a move his former attorney described as “very rare” for such a young defendant.

“He didn’t qualify for the state hospital because he didn’t show all the symptoms of being a complete whacko,” says Bickart, who adds that Kohlhepp’s birth father put him up for adoption when he was younger because “he couldn’t control” his son’s violent temper and unpredictable outbursts.

(Kohlhepp has reportedly not retained an attorney who could respond to the allegations against him, and sheriff’s officials have told PEOPLE an interview from jail is “not going to happen,” citing the ongoing investigation. It is unclear if he has pleaded to his new charges.)

Todd Kohlhepp - News
Credit: Tim Kimzey/The Spartanburg Herald-Journal/AP

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In recommending that the teenager be tried in adult court, an Arizona judge overseeing the case wrote, in documents obtained by PEOPLE, “At less than the age of 9, this juvenile was impulsive, explosive, and preoccupied with sexual content. He has not changed. He has been unabatedly aggressive to others and destructive of property since nursery school. He destroys his own clothing, personal possessions and pets apparently on whim and caprice.

“Approximately six years of intervention in fifteen years of life have resulted in abysmal failure. Twenty-five months of the most intensive and expensive professional intervention, short of God’s, will provide no protection for the public and no rehabilitation of this juvenile by any services or facilities presently available to the Juvenile Court.”

Bickart admits to being “terribly conflicted” while handling Kohlhepp’s case because he realized what the “big, very bright” teenager might one day be capable of.

Apparently, so did the Maricopa County Superior Court judge who eventually sentenced Kohlhepp to 15 years in prison after a plea deal was reached that involved the youth pleading guilty to kidnapping and registering as a sex offender.

“I never thought he’d be the type to shoot up a school,” insists Bickart. “but I thought he’d focus [his violence] on women.. . . I don’t think [his psychopathic tendencies] truly matured until he got older and got out of prison, but he got developed in prison, believe me.”