A woman and a man found each other through an online posting looking for a partner -- to end their lives together.
Shortly after meeting in person, Joanne Lee and Stephen Lumb got into Lee's car and committed suicide.
The double suicide of two strangers has stunned Great Britain where it occurred and surprised suicide experts.
"It's very, very unusual," said Essex Police press officer Heather Watts who said she's never seen anything like this in her 20 years on the police force. "We have had double suicides, but not under the circumstance where they'd never met in person....I saw it as a sign of the times when people meet and do things on the Internet."
"People meeting in an online forum to enter into a pact is very rare," said Nicola Peckett, spokeswoman for Samaritans, a prominent suicide hotline in Britain.
Lee, 34, and Lumb, 35, are believed to have met on an internet forum that discusses suicide when she put up a notice seeking a partner to help her die.
"I haven't the strength to do this alone. I have all the ingredients and want to do it ASAP," Lee wrote, according to London's Daily Mail.
Lumb responded to her internet request and drove 200 miles to meet her for the death date in Essex. Once together, the pair sat inside Lumb's car and awaited their end by lethal gas, a homemade mix of chemicals they'd stirred up in a bucket.
They were well-dressed and left notes on the car windows warning of toxic chemicals inside. The bodies were removed from the car by firemen in airtight suits.
Lee suffered from depression and anorexia, and had discussed her suicide plans for weeks on online forums where people offered advice on how to complete the task and gave encouragement in her efforts.
Lumb wrote a farewell message on one of the sites where he said, "I'm just saying goodbye im ctb today, and to all you people suffering i hope you find what your looking for."
"CTB" means "catch the bus" and is a phrase used online to indicate suicide.
Peckett said online sucide sites can be dangerous. "Two distressed people get into a place where what they do is they exacerbate each other's suicidal feelings, they perpetuate each other's feelings that life is pointless," Peckett said.
The deaths were a surprise to family members, including Lumb's father Melvyn who lived at home with his son.
"It is a complete shock, I never expected anything like this," Melvyn Lumb told the BBC. "I loved him, I will miss him every day of my life. I will miss him every minute of every day. I thought the world of him. I couldn't have had a better son."
Lee's family said in a statement that Lee, who lived alone with two cats, was receiving treatment for her depression and anorexia.
"We thought that her condition was improving. She seemed more content than she had been in a long time. She seemed happy." The family described Lee as a "shy, gentle, thoughtful and caring daughter, sister and friend."
Britain has about 6,000 suicides per year, low compared to many other countries like Japan. It also does not have a culture of suicide with strangers that has grown rapidly in Japan in recent years.
Samaritans says it receives one call every 60 seconds from someone who's suicidal. But unlike in the U.S. where guns are prevalent, the most common form of suicide here is hanging and there are only a handful of pact suicides per year.
The suicide rate in the U.S. is 11.5 per 100,000, about 35,000 people per year.