MANILA — In 2008, Jürgen Kantner and his partner were abducted from their sailboat, held for 52 days in Somalia and released after a six-figure ransom was reportedly paid.

Then he went back to Somalia to get his boat.

After three decades sailing the oceans, Mr. Kantner was a German on paper only. “Why should I go back to Germany, where I have nobody to help me?” Mr. Kantner was quoted as saying at the time. “I have no friends back home.”

Despite that ordeal, he and his partner continued to sail in dangerous waters. And on Monday, the Philippine and German governments identified Mr. Kantner, 70, as the man with shaggy white hair and an unkempt beard who was shown being beheaded in a video released by a Philippine militant group, Abu Sayyaf. It had demanded $600,000 in ransom for Mr. Kantner and had set a deadline of Sunday for the two governments to comply.

“We are deeply shaken at this inhuman and horrifying act,” Germany’s foreign ministry said in a statement. “We condemn the murder of this German in the strongest possible terms. There is no justification for such an act.”