Disbelief and a hint of fear flashed across Zuzana Čaputová’s face as the news broke.

After explaining to the Guardian how she would bolster the rule of law in Slovakia if elected president, Čaputová, a 45-year-old lawyer and the frontrunner in Saturday’s presidential poll, suddenly stopped short as an aide read out a headline from his phone: Marian Kočner, a multi-millionaire businessman, had been charged with ordering the murder of Ján Kuciak, a journalist who was investigating organised crime.

“Wow, I’m surprised, because I was on an opposing side in a legal conflict with Marián Kočner,” she said, startled momentarily into speaking in English, when she had previously been communicating through a translator.

The killings in February last year of Kuciak, a journalist with Actuality SK website, and his fiancee, Martina Kušnírová, provoked widespread revulsion and prompted Čaputová to run for office after thousands of Slovaks took to the streets demanding political change and an end to corruption.

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News of the charge against Kočner seemed to show hope for her faith in the power of popular participation to effect change. “People really need evidence and confirmation that these things will be investigated and that justice will be served to regain trust in the process,” said Čaputová, who has urged citizens to get involved in public life to preserve liberal democracy.

Čaputová was virtually unheard of until recently, but her soothing message of decency and civility – inspired, she says, by Gandhi’s book The Story of My Experiments With Truth, and by her political hero, the late former Czechoslovak president and anti-communist dissident Václav Havel – has propelled her into a commanding lead over a large field of candidates, leaving her heavily favoured to win an expected second-round ballot on 30 March.

Voters have rallied to her despite her publicly declared tolerance of LGBT rights such as civil partnerships and adoption, controversial positions in a predominantly Catholic country that forbids same-sex marriage and is known for conservative attitudes.

The election of such an avowedly pro-western figure, who openly favours the Nato alliance and EU membership, would provide welcome relief to liberals at a time when neighbouring countries, namely, the Czech Republic, Hungary and Poland, are led by populist politicians of varying stripes.

Slovaks point out that Čaputová would cut a contrasting profile with the Czech Republic’s pro-Moscow, migrant-baiting president Miloš Zeman – calling it a rare role-reversal in the relationship between the two countries that were once joined together in the former Czechoslovakia before its peaceful dissolution into separate independent states in 1993.

“When the Czech Republic joined Nato and the EU in the 1990s, we were left behind and [former US secretary of state] Madeleine Albright called us the black hole of Europe,” said Michal Katuška, a senior correspondent and presenter at Slovak national radio. “But now it looks like Slovakia will become, in neighbourhood terms, the half-eyed nation among the blind.”

Čaputová, however, cautioned that her election could be a double-edged sword, providing rightwingers with a stick to beat liberals. “I do believe that my election can serve as an inspiration or motivation to some elsewhere,” she said. “But it could also work the other way around.”

Yet, less than 48 hours before polls opened, official confirmation of Kočner’s suspected involvement in a crime that had already seen four other people charged with murder evoked darker thoughts, as Čaputová reflected on her past career as an activist-lawyer and the possibility that it had exposed her to potential danger.

The pair faced off when Čaputová used her legal skills to become the driving force behind a nine-year residents’ campaign against a landfill site, in which Kočner was involved, in her hometown of Pezinok, near Bratislava, the Slovak capital, which locals said leaked cancer-causing toxins.

The landfill was ordered closed in 2015 after a European court of justice ruling, earning Čaputová the prestigious the Goldman environmental prize and comparisons with Erin Brockovich, the campaigning lawyer played by Julia Roberts in an Oscar-winning Hollywood film.

“The names that are resurfacing in connection with this [Kuciak] case are those I remember from my time in Pezinok,” she said, speaking in her campaign headquarters in the offices of the recently formed Progressive Slovakia party, of which she is vice-chair, although she is officially running independently.

“I already knew that this is a high-stakes and very dangerous game. But perhaps it is only today that I fully appreciate how risky it all was. Even back then, he [Kočner] didn’t have a very good reputation. But this is something entirely different when it comes to the severity of the crime that he is charged with.”

With Kočner possibly heading for a long jail term, Čaputová now has new enemies to contend with – in the form of rumours and conspiracy theories posted on Facebook by what Bratislava-based thinktank, Globsec, describes as “pro-Kremlin disinformation channels”.

She has faced a barrage of attacks since the most recent survey, before a legally ordained two-week moratorium on pre-election polling that took effect on 2 March, showed her support at nearly 53%.

Some posts have voiced suspicions about her Goldman award, calling it the “Hillary Clinton prize” and suggesting, incorrectly, that she is Jewish. Others have questioned her status as a divorcee, spread rumours about her current partner, claimed that she is seeking to introduce “moral chaos” by imposing a pro-LGBT agenda, or smeared her as the candidate of George Soros, the billionaire philanthropist who has become a hate figure on the far right.

Andrej Danko, leader of the anti-western Slovak National party, a junior partner in the current governing coalition, posted a video on Facebook calling Čaputová an “unknown girl who has been created by PR companies”.

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Čaputová said she had been shocked by the intensity of the attacks, which she said were “full of hatred and based on lies” but was determined not to respond in kind.

There are signs, however, that the tactics are resonating with some.

In the Mlsná Emma coffee shop in Pezinok, Juraj, a 30-year-old land surveyor in a black baseball cap, said he would not vote for Čaputová despite knowing members of her family personally.

“Her view of the world is different from mine. It’s too liberal,” he said. “Someone has taken a lot of money and spent it on her election campaign and she is getting bigger and bigger – and I don’t know why. She has a really good PR management.”

In reality, Čaputová – who says her campaign has funded by small donations from ordinary citizens totalling €200,000 – owes her popularity partly to the current liberal president Andrej Kiska’s decision not to seek re-election. She has been further boosted by the decision of another liberal candidate, Robert Mistrík, to withdraw to avoid splitting the vote. A third contender, Maroš Šefčovič, an EU commissioner, has been undermined by perceived association with the governing left-wing Smer party, which has been in government for 10 of the past 12 years but has become increasingly unpopular as allegations of malfeasance have multiplied.

Šefčovič, though nominally independent and not a Smer member, only agreed to stand after the party failed to find other candidates and has accepted its funding. He is widely seen as beholden to Robert Fico, the former Smer prime minister who was forced to resign after Kuciak’s murder but is believed to still control party and government affairs.

Šefčovič is in a contest with Štefan Harabin, a judge and former head of the supreme court who has emerged as the favoured candidate of the far right, to finish second on Saturday’s ballot and enter the run-off - which is virtually certain because Slovakia’s constitution requires the president to be elected by at least 50% of all eligible voters, not just those who turn out.

Voter disenchantment with the EU over migrations fears could favour Harabin, who has promoted baseless rumours that large numbers of immigrants are waiting to cross Slovakia’s borders or are being housed within the country and who has been praised by the same disinformation sites that are attacking Čaputová.

Igor Daniš, a Slovak commentator and analyst, warned that an online smear campaign could enable Harabin to threaten Čaputová in a two-way contest. Others predict such a scenario would prompt a high turnout from voters determined to keep Harabin out.

Čaputová, who practises Zen-Buddhist yoga to keep her emotions in check, said she would be unfazed by further attacks. “I have absolute faith in the ability and maturity of Slovak voters to distinguish between what is true and what is not,” she said.