Homolka later stole the anesthetic agent halothane from the Martindale Veterinarian Clinic where she worked. On December 23, 1990, after a Homolka family Christmas party, Bernardo and Karla Homolka drugged Tammy Homolka with the animal tranquilizers. Bernardo and Karla Homolka raped Tammy while she was unconscious. Tammy later choked on her own vomit and died. Before calling 911, they hid the evidence, redressed Tammy, who had a chemical burn on her face, and moved her into her basement bedroom. A few hours later, Tammy was pronounced dead at St. Catharines General Hospital without having regained consciousness. Bernardo told police he tried to revive her, but failed, and her death was ruled an accident.

The Crown had applied for the ban imposed on July 5, 1993, by Mr. Justice Francis Kovacs of the Ontario Court (General Division). Homolka, through her lawyers, supported the ban, whereas Bernardo’s lawyers argued that he would be prejudiced by the ban since Homolka previously had been portrayed as his victim. Four media outlets and one author also opposed the application. Some lawyers argued that rumours could be doing more damage to the future trial process than the publication of the actual evidence.

On May 18, 1993, Homolka was arraigned on two counts of manslaughter. Bernardo was charged with two counts each of kidnapping, unlawful confinement, aggravated sexual assault and first-degree murder as well as one of dismemberment. Coincidentally, that day Bernardo’s original lawyer, Ken Murray, first watched the rape videotapes. Murray decided to hold onto the tapes and use them to impeach Homolka on the stand during Bernardo’s trial. Neither Murray nor Carolyn MacDonald, the other lawyer on the defence team, were deeply experienced in criminal law and it was only over time that their ethical dilemma showed itself also to be a potentially criminal matter, for they were withholding evidence. By October 1993, he and his law partners had studied over 4,000 documents from the Crown. Murray has said he was willing to hand over the tapes to the Crown if they had let him cross-examine Homolka in the anticipated preliminary hearing. The hearing was never held.

Homolka was tried on June 28, 1993, though the publication ban the court had imposed limited the details released to the public, who were barred from the proceedings.

Murray said the videotapes showed Homolka sexually assaulting four female victims, having sex with a female prostitute in Atlantic City, and at another point, drugging an unconscious victim. In February 1994, Homolka divorced Bernardo.

On September 12, 1994, Cooper attended Bernardo’s trial and advised Justice Patrick LeSage of the Ontario Court’s General Division, lawyer John Rosen, who replaced Murray as Bernardo’s defence counsel, and the prosecutors about what the law society had directed Murray to do. Rosen argued that the tapes should have been turned over to the defence first. Murray handed the tapes, along with a detailed summary, to Rosen, who “kept the tapes for about two weeks and then decided to turn them over to the prosecution.”

“The law society directed Murray in writing to seal the tapes in a package and turn them over to the judge presiding at Bernardo’s trial. The law society further directed him to remove himself as Bernardo’s counsel and to tell Bernardo what he had been instructed to do,” Murray said in a statement released through Cooper in September 1995.

After her 1995 testimony against Bernardo, when Homolka returned to Kingston’s Prison For Women, her mother, Dorothy Homolka, started to suffer annual breakdowns between Thanksgiving and Christmas. The collapses were severe enough that she was hospitalized, sometimes for months at a time. While at Kingston Homolka began correspondence courses in sociology through nearby Queen’s University which initially caused a media storm. Homolka was required to pay all fees, as well as her personal needs, from her fortnightly income of about $69, although, she told author Stephen Williams in a subsequent letter, “I did get some financial assistance”. Homolka later graduated with a Bachelor’s degree in Psychology from Queen’s. News of Homolka’s educational efforts were greeted in the media with disdain: “Nothing has changed. Concepts of remorse, repentance, shame, responsibility and atonement have no place in the universe of Karla. Perhaps she simply lacks the moral gene,” wrote Globe columnist, Margaret Wente.

In 1997, Lynn Crosbie, Canadian poet, novelist and cultural critic, published Paul’s Case, termed a “theoretical fiction”. After systematically analyzing the couple’s crimes, it provided an examination of the cultural effects of the shocking revelations and controversy surrounding their trial.

In 1999, Toronto Star reporter Michelle Shephard came into possession of copies of her application to transfer to the Maison Thérèse-Casgrain, run by the Elizabeth Fry Society, and published the story noting the halfway house’s proximity to local schools, hours before the Canadian courts issued a publication ban on the information. Homolka sued the government after her transfer to a Montreal halfway house was denied.

While being evaluated in 2000, Homolka told psychiatrist Robin Menzies that she did not consider the relationship to be homosexual, as Véronneau “saw herself (sic) as a man and planned to undergo a sex operation in due course,’ the psychiatrist wrote.” Psychiatrist Louis Morisette, meanwhile, noted in his report that Homolka “was ashamed of the relationship and hid it from her parents and the experts who examined her. The psychiatrist mentions in his report that under the circumstances, the relationship was not abnormal.”

A 2000 episode of Law & Order (Season 10 Episode 15, “Fools For Love”) was inspired by this case.

In December 2001, Canadian authorities determined that there was no possible future use of the videotapes. The six videotapes depicting the torture and rape of Bernardo’s and Homolka’s victims were destroyed. The disposition of the tapes of Homolka watching and commenting on the tapes remains sealed.

In 2001, Homolka was transferred to the Ste-Anne-des-Plaines Institution, a maximum security prison in Quebec.The Toronto Sun reported that, while there, Homolka began a sexual relationship with Jean-Paul Gerbet, a convicted murderer being held in the men’s unit of the facility.

According to former inmate and Homolka confidante Chantel Meuneer, the Sun reported, Homolka and the inmate stripped at a flimsy fence, touched one another sexually and exchanged underwear. At the same time, Meuneer told the Sun, Homolka was still in a same-sex relationship with Lynda Véronneau, who had spent $3,000 on her at Victoria’s Secret. On December 6, 2001, only seven days before Homolka dumped Véronneau, Meuneer said she asked Homolka why she continued her lesbian relationship while being in love with a man. Meuneer recalls Homolka saying, “I don’t let go right now because I want my clothes and I want my computer.”

Where other inmates might apply for parole at the first opportunity, Homolka refrained from doing so. “Because she was deemed a risk to reoffend, she was denied statutory release two-thirds of the way through her sentence,” Maclean’s reported in explaining what had exempted Homolka from the parole restrictions meant to ease an offender’s integration into mainstream society. In 2004, the Canadian Broadcasting Corporation noted that “The National Parole Board has ruled that Karla Homolka must stay in prison for her full sentence, warning that she remains a risk to commit another violent crime.” While the NPB noted that she had made some progress toward rehabilitation it expressed concern regarding her relationship with convicted murderer Jean-Paul Gerbet. The NPB reprimanded Homolka: “you have secretly undertaken an emotional relationship with another inmate, and evidence gathered seems to indicate that this relationship rapidly became sexual,” the panel stated. As a result it decided to keep her in prison.

In 2004, Quantum Entertainment released the film Karla (which had the working title Deadly), starring Laura Prepon as Homolka and Misha Collins as Bernardo. Tim Danson, lawyer for the French and Mahaffy families, was given a private screening, and announced that the families had no objection to the film’s release. Nevertheless, Ontario Premier Dalton McGuinty called for a boycott. The film was given a limited release in Canada by Christal Films.

Michael Bryant, Ontario’s Attorney General fought to get Homolka on the agenda at a meeting of Canada’s justice ministers. “He wants the federal government to expand the category of dangerous offenders to catch those slipping between the cracks.” “Bilingual and armed with a bachelor’s degree in psychology from Queen’s University, Homolka may choose to try to live a quiet life in Quebec, where her crimes are not as well known as they are in English-speaking Canada,” reported CTV in May 2005.

On June 2, 2005, the network said, “the Ontario Crown will ask a Quebec judge to impose conditions under Section 810 of Criminal Code on Homolka’s release.” “The French and Mahaffy families want even tighter restrictions on Homolka, including asking that she submit to electronic monitoring or yearly psychological and psychiatric assessment,” CTV said. These conditions are not allowed under Section 810 because they cross the line between preventive justice versus punitive measures, but “that’s why [Toronto lawyer Tim Danson, acting on their behalf] believes the families want the government to amend the Section.”

A two-day hearing was held before Judge Jean R. Beaulieu in June 2005. He ruled that Homolka, upon her release on July 4, 2005, would still pose a risk to the public-at-large. As a result, using section 810.2 of the Criminal Code, certain restrictions were placed on Homolka as a condition of her release:

On June 10, 2005, Senator Michel Biron declared that the conditions placed on Homolka were “totalitarian”, according to an interview with CTV Newsnet. Two weeks later, Biron apologized.

On July 4, 2005, Homolka was released from Ste-Anne-des-Plaines prison. She granted her first interview to Radio-Canada television, speaking entirely in French. Homolka told interviewer Joyce Napier that she chose Radio Canada because she had found it to be less sensationalist than the English-language media. She said that she had likewise found Quebec to be more accepting of her than Ontario. She affirmed that she would be living within the province but refused to say where. She said she had paid her debt to society legally, but not emotionally or socially. She refused to speak about her alleged relationship with Jean-Paul Gerbet, a convicted murderer serving a life sentence at Ste-Anne-des-Plaines. During the interview, her solicitor, Sylvie Bordelais, sat beside Homolka; however, she did not speak. Homolka’s mother was also present but off-screen, and was acknowledged by Homolka.

The national media reported in July 2005 that Homolka had relocated to the Island of Montreal. On August 21, 2005, Le Courrier du Sud reported that she had been sighted in the South Shore community of Longueuil, across the St. Lawrence River from Montreal.

On November 30, 2005, Quebec Superior Court Judge James Brunton lifted all restrictions imposed on Homolka, saying there was not enough evidence to justify them. On December 6, 2005, the Quebec Court of Appeal upheld Brunton’s decision. The Quebec Justice Department decided not to take the case to the Supreme Court, despite Ontario’s urging.

Lynda Véronneau together with writer Christiane Desjardins, wrote Lynda Véronneau: Dans L’Ombre de Karla, on the topic of her relationship with Homolka while in prison, published in 2005 by Les Éditions Voix Parallèles.

TVA reported on June 8, 2006 that Homolka’s request to have her name changed was rejected. She had attempted to change her name legally to Emily Chiara Tremblay (Tremblay being one of the most common surnames in Quebec).

Sun Media reported in 2007 that Homolka had given birth to a baby boy. Quebec Children’s Aid said that despite Homolka’s past, the new mother would not automatically be scrutinized. Several nurses had refused to care for Homolka before she gave birth. On December 14, 2007, CityNews reported that Homolka had left Canada for the Antilles so that her then one-year-old could lead a “more normal life.” She later had 2 more children.

In a 2008 letter of apology to her family, she continued to blame Bernardo for her misdeeds: “He wanted me to get sleeping pills from work… threatened me and physically and emotionally abused me when I refused… I tried so hard to save her.” Tim Danson, lawyer for the victims’ families, has said that she has never apologized to them.

On January 11, 2008, the Canadian Press reported that letters written by Homolka to Lutczyn had been pulled from eBay, where they had reached $1,600 with a week to go. Lutczyn said she did not want them any more.

On April 19, 2010, The Vancouver Sun reported that Homolka would be eligible to seek pardon for her crimes in the summer of 2010. Offenders convicted of first- or second-degree murder or with indeterminate sentences cannot apply for a pardon due to the fact that their sentences are for life, but Homolka was convicted of manslaughter, and received less than the maximum life sentence, making her eligible. If she had been successful her criminal record would not have been erased but would have been covered up in background checks, except those required for working with children or other vulnerable people.

On June 16, 2010, Public Safety Minister Vic Toews said an agreement had been reached between all federal parties to pass a bill that would prevent notorious offenders like Karla Homolka from obtaining a pardon.