Guitarist Mark St. John started his recording career with a bang, joining Kiss for the band's hit 1984 Animalize LP, but he struggled to build career momentum in the years following his exit from the lineup — and ultimately slipped into obscurity before dying under murky circumstances in April 2007.

The third guitarist to officially pass through the Kiss ranks, St. John joined the band during a period of professional and creative flux. As guitarist Paul Stanley has since admitted, he and bassist Gene Simmons were on separate wavelengths during the early part of the decade, with Simmons focused on branching out into films while Stanley remained committed to the band. Having already weathered the departure of founding guitarist Ace Frehley and the short-lived turmoil of Vinnie Vincent's brief stint, the group needed a measure of consistency — something St. John initially seemed able to provide.

Unfortunately, it soon became apparent that he wasn't a natural fit. As St. John later told Kiss Asylum, the group's fragmented state meant that he was alone in the studio with "a couple of engineers" during his first sessions — and Stanley and Simmons were "horrified" to hear what he'd done when they returned. "They got all kind of weird about that and decided that they had to be there all the time while I was playing guitar, watching over me," he claimed. "It was one of those dog-on-a-leash things."

Simmons and Stanley, unsurprisingly, told a different story. "My classic story with Mark is that during the making of Animalize I sent him home one night to come up with a solo to one of the songs. And the next day he came back and played me something that was at least a start. Then I said, 'Play it again.' And he said, 'I can’t,'" alleged Stanley. "The guy could never play the same thing twice, because he was just puking notes. There was no structure to any of it."

Although they were able to make it work well enough to finish the Animalize LP, things grew even more difficult once it was time to take the band on the road. St. John developed painful swelling in his extremities and was diagnosed with Reiter's syndrome, a form of arthritis; obligated to fulfill its live commitments, the group brought in guitarist Bruce Kulick to sub for St. John, who ultimately was only able to perform one and a half concerts with the group.

"We used to warm up backstage together," Kulick told Ultimate Classic Rock. "As much as in a way we were competing, I put that out of my head. I wanted him to be comfortable. I wasn't gonna do a Tonya Harding on him or anything." Whether it was due to health, musical or personal compatibility, it soon became clear Kulick was destined for the job. In late 1984, St. John was out of the band permanently. "The arthritis thing was really a cover up for the other reasons, you know what I'm trying to say? I think a lot of people might know that," St. John shrugged. "I can still play guitar. The situation was a meeting of East meets West type of thing."

Proving he definitely could still play guitar, St. John quickly embarked on a series of musical projects with a variety of players, including ex-Black Sabbath singer David Donato (with whom he co-founded White Tiger) and fellow Kiss vet Peter Criss. Unfortunately, none of those possibilities ended up panning out, and by the late '90s, he'd been all but forgotten outside the Kiss community — although he remained active, releasing an EP in 1999 and an instrumental album four years later.

As he fought for musical recognition beyond his brief Kiss contribution, St. John battled personal demons as well. In 2006, he was arrested for possession of drug paraphernalia and charged with attempted destruction of evidence, and ended up serving a brief sentence in a Southern California prison. In the context of the many other run-ins various professional musicians have had with the law over the years, St. John's incarceration seemed more than minor — but it'd cast a tragic shadow over his death the following year.

Initial reports attributed St. John's death to an "apparent brain hemorrhage," but by the following year, evidence surfaced linking his condition to injuries sustained in a beating he suffered while he was in lockup. The Orange County Weekly uncovered allegations of a network of guard-sanctioned inmate abuse, as well as St. John's inmate file, which included a request to be transferred out of fear of retribution for stealing "crackers out of another inmate's property box."

Those allegations were ultimately the basis of a reported investigation conducted by the county sheriff's department, which ultimately seems to have come to naught. It all added up to a sad, strange end to a life and career that once seemed destined for so much more — and for St. John's former bandmates, a reminder of what might have been. "Mark was a great guitarist and a good man," Simmons told Kiss fans after hearing of St. John's death. "He will be missed."