Eighty-eight people in the UK died after buying a poisonous substance from a seller in Canada, the National Crime Agency (NCA) has said.
The NCA says it cannot confirm the chemical was the direct cause of the deaths in the UK but is investigating potential criminal offences.
British police have been making welfare visits to hundreds of addresses to trace buyers across the country.
Kenneth Law was arrested in May and is accused of assisting suicide in Canada.
Mr Law, 57, is thought to have run a number of websites selling equipment to assist suicide.
That also included a poisonous chemical which he sent to customers in more than 40 countries.
Peel Regional Police said they began investigating the case in April following the sudden death of an adult in the Toronto area.
Since Mr Law’s arrest, police forces across the UK have been making checks on everyone who ordered the substance.
The NCA, which was coordinating the checks, said that 232 people in the UK had been identified as buying from Mr Law over a two-year period.
The agency says 88 of them later died but it could not confirm a direct link with the death.
NCA deputy director Craig Turner said: “Our deepest sympathies are with the loved ones of those who have died. They are being supported by specially trained officers from police forces.
“In consultation with the Crown Prosecution Service, the NCA has taken the decision to conduct an investigation into potential criminal offences committed in the UK. This operation is under way.”
Tom Parfett, from Maidenhead, was 22 when he ended his own life in October 2021 after buying the chemical from Mr Law.
His father David Parfett is angry at what he sees as police failures.
“It’s important for families to understand what has happened and why policing worldwide allowed this scale of deaths despite clear warning signs,” he said.
Mr Parfett fears there other suppliers out there and unregulated websites promoting suicide.
“What can be done immediately to close down internet sites that prey on vulnerable young people and prosecute the people who take pleasure in helping others take their own life?” he asked.
In a separate interview with BBC Radio 4’s Today programme, Mr Parfett said his son had discussed taking his own life with people he met online in communities set up to discuss the subject, and was encouraged to do so by some.
He added: “We have to accept that in the modern age, people can find like-minded people to discuss even the most difficult problems…those communities are unregulated and causing a huge amount of harm.”
Mr Parfett called for stronger action from police and policymakers to crack down on people selling poison, and for online communities targeting vulnerable people to be regulated.
He continued: “We need to be more sensitive around the risks that people like Tom have in society through their ability to find information online that is unchallenged.”
Mr Law, who is in custody, is due to appear in court again later this month.
Under the country’s criminal code, counselling or aiding a person to die by suicide can result in a 14-year prison sentence.
If you’ve been affected by self-harm or emotional distress, help and support is available via the BBC Action Line
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