Jason Frandi described himself as "just lovely" to a Southland solo mother he had a texting relationship with in the months before he killed a Czech backpacker.
The 31-year-old said Frandi had written a letter in reply to a personal column advertisement she had put in a publication earlier this year.
"He did honestly sound too good to be true."
In that letter, Frandi described himself as having a GSOH - "good sense of humour" - and gave his address and phone number for future contact.
The Southland woman said that as part of their burgeoning relationship she had exchanged hundreds of texts, including several pictures, with the pair often texting late into the night.
After several weeks of non-communication she decided to call him for the first time when he was named in connection with the murder of Dagmar Pytlickova, 31.
"I just saw his photo, and thought, 'That's him.'
"I felt so sick after reading the paper ... that could have been me."
Frandi is believed to have assaulted and murdered Ms Pytlickova before taking his own life.
Frandi and Miss Pytlickova's bodies were found in a forestry block near the South Canterbury town of Waimate, where Frandi lived. It was revealed last month that police were hunting for the convicted kidnapper shortly before the bodies were discovered.
The Southland woman said she was shocked by the news, which left her unable to sleep for several days and wondering what might have happened if she had called to meet him for the first time.
She had removed her advertisement from the publication, as well as another online dating site, on the day she found out about Frandi, and is now warning others looking for love to be careful.
"I am just going to stick to myself, I reckon."
NetSafe chief technology officer Sean Lyons said people were advised to do online background checking on people they might be interested in getting involved with. When meeting someone for the first time, it was advisable to meet during the day and even take someone with you, he said.
Police are still trying to piece together the final movements of Frandi and his victim.
Detective Senior Sergeant Marion Neill said officers were focusing on the movements of Ms Pytlickova and Frandi on Saturday, May 26 - the day before the bodies were found. He said the last confirmed sighting of Frandi was in Waimate at 12.17pm.
When meeting someone online:
* Do as much research on an individual as you can. Look at Facebook, LinkedIn, message boards on dating sites to see if they have been mentioned, and whether what they say about themselves is true.
* If planning to meet up with someone for the first time, make sure you do it in the daytime, in a public place, and take someone with you for security.
- Otago Daily Times