A drug dealer who used the dark web to supply customers - including four that later died - with the powerful synthetic opioid fentanyl has been jailed for eight years.
Kyle Enos, 25, of Newport, south Wales, sold the drug to 168 people in the UK, Europe and the US between May 2016 and May 2017.
Cardiff Crown Court heard that following his arrest, police went through Enos's customer database due to the "potentially lethal effects" of fentanyl.
Rob Osborne reports:
Four people on his database had died but it cannot be proven that the fentanyl supplied by Enos was related to their deaths.
The court heard Jonathon Robinson, 25, from Northumbria, was found dead at home, while university student Jack Barton, 23, died in Cardiff in January 2017.
Aaron Rees, 34, from Ammanford in Carmarthenshire, Wales, was found dead last March. The fourth person, who was not named in court, died in Scotland.
Sentencing Enos, Judge Eleri Rees, said the drug "is 25 times more powerful than heroin as is evidenced by the deaths of at least four young people who were your customers.
"None of those deaths can be attributed to Fentanyl supplied by you, but it is evidence of how dangerous a drug it is".
In August Enos admitted importing, supplying and exporting fentanyl.
More than 100 people from around the world had bought fentanyl from Enos after he imported the drug from China.
Fentanyl is used as a super strong painkiller for cancer patients and is often prescribed in patches, nasal sprays, lozenges or tablets.
National Crime Agency statistics show that since December last year 60 drug-related deaths were known to be linked to fentanyl or a related substance.
Speaking after the sentence Colin Williams from the National Crime Agency said Enos had "played Russian Roulette" with customer's lives.
He said: "The threat posed by synthetic opioids is not new and we have seen a number of drug related deaths linked to fentanyl and carfentanyl in recent months.
"We have taken action with partners in the UK and overseas against people we believe are responsible for playing Russian roulette with the lives of drug users by mixing synthetic opiods with drugs such as heroin."
The judge said the delay in sentencing Enos was to consider whether further charges would arise from the deaths of four of his customers, as well as to obtain more information about the effect of fentanyl.
Charges will not be brought against Enos for the deaths that occurred in England and Wales, but investigations are continuing in Scotland.