Irishman Ibrahim Halawa has said that the 1,000 days he has spent in prison in Egypt have felt like 1,000 years.
In a letter to his family the Dublin man said he is suffering while other prisoners have died by suicide.
The 20-year-old was arrested in Cairo 1,001 days ago while there were political protests ongoing, and he is now awaiting a trial and a potential death penalty.
His family held a demonstration in Dublin yesterday to mark the 1,000 days he has spent in prison.
His sister, Somaia Halawa, shared a letter he sent the family last week.
"One thousand days with 1,000 different stories. Sadly, not the type of joy, laughter and smiles. But rather the type full of suffering, pain, torture, tears, abuse, suicide, and death," he wrote.
"One thousand days that have felt like 1,000 years, not only for me but for hundreds behind bars. Some have lost hope and written 'the end' on their story, but I leave many blank pages to be filled."
Somaia Halawa said she wants to see more serious and assertive action to free her brother. "We want to call on an end to this nightmare," she said.
"This Irish student has been imprisoned in Egypt with no conviction, no fair trial, no adequate access to a lawyer, has been electrocuted, beaten, spat on and moved without his family's knowledge."
Amnesty International's executive director Colm O'Gorman said the organisation has conducted a review of the prosecution's evidence and concluded that Mr Halawa could not have committed the crimes with which he has been charged.
His mass trial has been delayed 13 times and is now due to take place on June 29.
"Similar mass trials have seen hundreds of defendants convicted without ever having had an opportunity to present a defence, following hearings which lasted mere minutes, at the end of which hundreds were sentenced to death," Mr O'Gorman said.
He also criticised the Egyptian Ambassador to Ireland's recent comments about the case. "The Ambassador's comments in relation to Ibrahim's case have been nothing short of outrageous," Mr O'Gorman said.
The Department of Foreign Affairs said every effort was being made to secure his release.