Ader was in Canada at the time of his arrest on June 11 by the RCMP's Integrated National Security Enforcement Team (INSET.)
The RCMP described him as the "main negotiator" in the hostage-taking of Lindhout and her Australian colleague, Nigel Brennan.
Lindhout and Brennan were kidnapped near Mogadishu, Somalia on August 23, 2008. The RCMP said Friday it began a criminal investigation at that time.
The investigation, named Project Slype, was carried out with the cooperation of the government of Somalia. The suspect was located in Somalia, but arrested in Ottawa following undercover operations, surveillance and wiretaps.
The RCMP did not disclose how or why Ader was in Ottawa.
"Because the investigation was conducted on an international basis, it did create some challenges," said RCMP Assistant Commissioner James Malizia.
The RCMP said the Canada Border Services Agency, the Foreign Affairs department and the Australian Federal Police collaborated on the investigation.
Lindhout was released on Nov. 25, 2009 after more than a year in captivity. She has written and spoken extensively about the abuse she endured during that time.