On March 21, 1994, Gillis murdered his first victim, 81-year-old Ann Bryan, whose residence (an exclusive retirement home) he entered when she left the door unlocked for her nurse. He tried to rape her, but when she started screaming after he touched her, he quickly slashed her throat and then stabbed her repeatedly, nearly decapitating and disemboweling her in the process. The following year, he and Terri moved in together, and she eventually realized his addiction to pornography, but decided to ignore the issue, although she didn’t realize what kinds of pornography Gillis specifically took a liking to. She continued to ignore the issue when he showed her pictures of dead women, which she was disgusted at, but otherwise, the two maintained a good relationship. On January 4, 1999, almost five years after the murder of his first victim, Gillis, allegedly bored from the inactivity, struck again, killing Katherine Hall, a prostitute he lured into the car with the promise of oral sex; he tried to kill her by strangling her with a zip-tie, but when she tried to escape, he instead stabbed her to death before undressing her and mutilating her body. Four months later, he began stalking Hardee Schmidt, whom he spotted jogging in the southern area of Baton Rouge; after three weeks, he found her jogging again and hit her with his car, knocking her into a ditch. Gillis then tied a zip-tie tightly around her neck and took her to an isolated area, where he raped and killed her before placing her body in a truck, where it remained for two days until he dumped it in a bayou located off of Highway 61 at St. James Parish, where it was discovered soon afterward. On November 12, he killed Joyce Williams and took her body to his home, where he mutilated it and engaged in cannibalism. He then dumped her body, where it wouldn’t be discovered until January 2000.
After killing three more victims from 2000 to 2003 (during which another serial killer, Derrick Todd Lee, whom Gillis admired, was active), Gillis murdered his eighth and final victim, 43-year-old Donna Johnston, on February 26, 2004. After taking 45 pictures of her body, he took it to another location and dumped it, but took the time to pose it first. On March 3, a task force was established to look into the murders of Johnston, two other victims of Gillis’s, and also other victims when certain cases couldn’t be linked to Lee, who had been apprehended the previous year for his own killings, which sparked fears of one or two other serial killers being still at large. In April, tire tracks found at the dump-site of Donna Johnston were traced to a certain model. On April 28, investigators interviewed and got DNA swabs from a number of people who owned vehicles that had that specific tire model, including Gillis. When Gillis’s DNA sample matched the DNA found on the hairs of two of his victims, police arrested him the next day in front of Terri, to whom he apologized during the arrest. Later that day, he confessed to his murders and his house was subsequently searched. Among the items recovered were newspaper clippings of Carrie Yoder, the final victim of Derrick Todd Lee, and a computer file titled “DTL” (Lee’s initials), which stored news and information about Lee’s crimes; Gillis would go on to allege that he feared being “outdone” by Lee. After evaluating his confessions and giving him various charges that changed multiple times, investigators finally charged him for the murders of Katherine Hall, Johnnie Williams, and Donna Johnston, which he stood trial for on July 21, 2008. On July 31, he was eventually found guilty of all charges and sentenced to life in prison without parole after the jury made a deadlock during the penalty phase. On August of the previous year, he pleaded guilty to second-degree murder and was subsequently convicted in the murder of Joyce Williams. On February 17, 2009, Gillis pleaded guilty to the murder of Marilyn Nevils, which he received another life sentence for.