The students' bedsit was set alight after the crime
A man accused of murdering two students, who were stabbed hundreds of times, had depression and wanted psychiatric treatment, a court heard.
Laurent Bonomo and Gabriel Ferez, both 23, were murdered in a bedsit in New Cross, south-east London, in June 2008.
Dano Sonnex, 23, of Peckham, south London, and Nigel Farmer, 33, of no fixed address, deny two counts of murder, arson and false imprisonment.
At the Old Bailey, Mr Farmer's mother said events had left her "torn apart".
The mother-of-six, originally from Ireland, who has a different surname from her son and cannot be named for legal reasons, said: "My son is in the dock and I know the family of Laurent and Gabriel are sitting a few feet away from me."
She added: "I'm torn apart, it's tearing my heart inside. I'm his mum, but I must know the truth of what happened to Laurent and Gabriel and what happened to my son that weekend."
Giving evidence, she said Mr Farmer told her he feared what he might do if he did not receive psychiatric treatment in the weeks leading up to the crime.
However, she told the jury she did not believe that her son would "go and kill somebody".
The court heard that Mr Farmer, a father-of-two, became depressed after his long-term relationship ended and he twice tried to commit suicide.
Firefighters found the bodies of the two students in a scene of "almost unimaginable horror", the court also heard.
The pair, who had been studying biochemistry at Imperial College, had been tied up during the robbery.