BERLIN (AP) — Germany's Interior Ministry said Friday it will "leave no stone unturned" in trying to determine how a German army officer managed to register as a Syrian asylum-seeker without being detected.

Conceding that mistakes were made, a ministry spokesman said every effort was being made to uncover how the 28-year-old lieutenant duped authorities, received a place in a refugee home and collected financial aid.

"This decision was wrong," the spokesman, Tobias Plate, told reporters in Berlin. "The Interior Ministry and the Federal Office for Migration and Refugees will now leave no stone unturned until we known how this could happen, and if there were deficiencies, these are removed."

Franco A. was arrested Wednesday and charged with preparing an act of violence that investigators believe he planned to blame on refugees. He and a 24-year-old German student, who also was arrested, had allegedly expressed anti-foreigner views, according to electronic devices seized by investigators.

A., whose full name wasn't released due to German privacy rules, allegedly stashed a pistol in a Vienna airport bathroom and was taken into custody when he went to retrieve it in February. He was freed, but Austrian authorities informed their counterparts in Germany, and a fingerprint match showed he registered as a refugee in November.

Germany by then had seen the arrival of hundreds of thousands of asylum-seekers — many of them fleeing war and persecution in the Middle East. It also had tightened vetting procedures following a series of violent attacks in Germany and neighboring countries that were carried out by registered refugees.

Plate rejected the notion that there were "structural problems" in the procedures for vetting asylum-seekers.

"Instead, it seems that established and required security measures, which all those involved should have known about, weren't followed," he said.

A defense ministry spokesman, Jens Flosdorff, said the officer had passed routine security checks since joining the army eight years ago and hadn't aroused any suspicions.