The 30-year-old husband is defending himself in a Malmö court on Thursday against charges that, as a member of the banned terror group Islamic State, he carried out an arson attack against a Shia Muslim centre.
The man's defence lawyer, Lars Edman, said a tape of the questioning of the man's 25-year-old wife, showed Säpo putting the witness under extreme pressure.
"Do you want to have an insecure situation with him and then leave Sweden together with him, or do you want to have a safe situation here with your brother," the Säpo investigator said. "Yes, turn him in and then you get to stay".
I have never seen pressure on a witness so explicit as this," Edman told Swedish Radio. "What I'm reacting against is this threat that she will not be able to stay in Sweden."
At no point in the record of the questioning is the woman informed that she is not required to answer the police's questions. In Sweden one cannot be forced to witness against a close relation.
On the contrary, one of the interviewers falsely informs her that she is committing a crime if she doesn't reveal what she knows.
Swedish Radio contacted an independent lawyer, Thomas Olsson, who confirmed that Säpo appeared to be misleading the woman into believing that Säpo has the right to expel people from Sweden.
"They are trying to get information out of her through threatening her with misleading information about how the law works, and partly threatening her that she is going to be expelled from Sweden," he said.
Säpo's press officer Nina Odermalm Schei refused to comment on this particular case.
"We are extremely careful to follow current rules," she said. "Everyone who we interview is informed of their rights. That's the way we work."