The parents of James Foley hoped they could negotiate with his captors before he was murdered.
As the hunt for the American journalist's killer – believed to be a British jihadist – continues, John and Diane Foley said their son will "live on".
The couple, who refer to their son as Jim or Jimmy, have also spoken about how they felt "very comforted and supported" after receiving a call from Pope Francis.
Speaking to Today in the US, Mr Foley said he was "excited" to see an email from their son's captors days before his brutal killing as they had not had any contact with them in months.
"We hadn't heard from Jim's captors since December and I actually was excited to see an email despite the conclusion that they would execute Jim.
"We, I, underestimated that point. I did not realise how brutal they were and I actually hoped we could engage in negotiations with them, if they were willing to send us any sort of communication because we'd had none prior," he said.
Mrs Foley added: "In December we had received several emails but then they stopped communicating so we were just anxiously waiting. We had established a special email and sent multiple messages hoping to engage them."
The mother of the murdered journalist said Pope Francis was "just so kind", with Mr Foley adding: "He offered us his personal prayer and we felt very comforted and supported in that regard."
A fund in James Foley's memory will be set up "so that his compassion can live on", his mother said.
She hailed all those who had prayed for her son, and said he was "held up by all that prayer".
Intelligence agencies on both sides of the Atlantic are working to identify the jihadist believed to have carried out the brutal killing, with expert analysts sifting through the gruesome footage for clues amid suggestions that the Islamic State (IS) extremist is from London.
The jihadist in the execution video is reported to be "John", the ringleader of a trio of UK-born extremists responsible for guarding Western hostages and nicknamed after members of The Beatles, with the two others dubbed Paul and Ringo according to the BBC.
In the video of the murder of Mr Foley, US president Barack Obama was warned that the life of American hostage Steven Sotloff hinged on his "next decision".
Meanwhile David Cameron faced calls for changes to the law in an effort to combat the threat of Islamist extremism in Britain following the murder.
Ministers, the police and MI5 are concerned about the threat from British nationals who have travelled to Syria and Iraq to fight for IS returning to the UK to carry on their jihad.
Hundreds of Britons are believed to have travelled to the region, and "significant numbers" are believed to have been involved in "terrible crimes" and "probably in the commission of atrocities" according to Foreign Secretary Philip Hammond.
The Prime Minister, before he resumed his family holiday in Cornwall, spoke about the threat to the UK when he briefly returned to Downing Street following the release of the video of Mr Foley's execution.
He said "far too many" Britons had travelled out there and promised to "redouble" efforts to stop them going to warzones.