A school was closed in southern Sweden on Tuesday as a wave of copycat threats swept the country.
"He had really not expected this much attention. He has no explanation other than an expression of deep regret," the man's defence counsel Ralph Ekman told news website SvD.se.
The student's reasons for issuing the threats on an internet forum on Sunday night remained a mystery on Tuesday.
In recent years, the man has studied at Linköping University and is currently enrolled at Chalmers University of Technology in Gothenburg, but he has never attended KTH.
"I have no answer as to why the threat was directed against KTH," Ekman said, adding that his client had assured him that the threat was not serious.
Swedish police sought the help of the FBI to trace the 33-year-old from the threatening post he published on the popular US-based internet forum 4chan.org. In his post he had explained that his girlfriend had recently broken up with him and that he wanted to die.
"On Monday I plan to take my gun ... to the school and shoot as many people as I can before the police come and shoot me," he wrote.
The poster also reportedly referred to recent school massacres in Finland.
"You'll see. I will beat that Finnish bastard's record, since Swedish police do not exactly seem to be the fastest at getting to the scene."
Sweden was hit by a wave of copycat threats on Monday and Tuesday in what experts described as a typical pattern for this type of offence.
A school in Västervik was closed as a precautionary measure after threats of a shooting were forwarded by mail on Monday. The decision was taken to keep the school closed on Tuesday as police had been unable to determine the threat's source.
In northern Sweden a 14-year-old boy took dynamite and a detonator to a school in Ramsele, and a 16-year-old in Piteå admitted to threatening to take a gun to school on Tuesday. Both were released after preliminary police interviews.
Later on Monday evening, a boy threatened to use a rifle to kill pupils and staff at a school in Borås in western Sweden. The school remained open under police surveillance on Tuesday.
"This type of crime has a contagion effect which is evidently greater than with other offences," said psychiatrist Ulf Åsgård to the Aftonbladet newspaper.