German prosecutors said Thursday they suspected a deadly attack on U.S. servicemen at Frankfurt airport by a gunman was motivated by Islamic extremism.
Arid Uka, 21, who worked at mail distribution center at the airport, cried "Allah Akbar" ("God is Greatest") before opening fire on a military bus at the busy airport, according to eyewitnesses quoted by German media.
Two U.S. Air Force Military Police were killed and two others were seriously injured.
The two airmen killed were named Thursday as Senior Airman Nicholas J. Alden, 25, of Williamston, S.C., and Airman First Class Zachary R. Cuddeback, 21, of Stanardsville, Va., according to Fox News Channel.
Alden was assigned to the 48th Security Forces Squadron, RAF Lakenheath, U.K., while Cuddeback was assigned to the 86th Vehicle Readiness Squadron, Ramstein AB, Germany.
New details about the gunman also emerged Thursday, with Spiegel magazine reporting that he made several unsuccessful attempts to travel to Afghanistan.
His father, Murat Uka, said he was shocked by the attack and apologized for his son's actions. "I am still in shock; I cannot believe what has happened," he told Reuters. "I am really, really sorry about what has happened."
The family's home in Frankfurt was surrounded by media. The family are ethnic-Albanians originally from Kosovo, a Muslim-majority country in southeastern Europe.
Regional interior minister Boris Rhein said the gunman told interrogators that he was working alone, and not as part of an organized terrorist group.
The minister described him as a "radicalized Islamist," Spiegel magazine said.
"In view of the circumstances, there is a suspicion that this was an act with Islamist motivation," prosecutors said in a statement.
A US official had previously told The Wall Street Journal that early indications suggested that the shooting was a terrorist assault and not a random act of violence.
A senior military official in Washington said the suspect has "some kind of Islamic ties, but we do not know exactly what those are or how deep they are." The official said it was too early to tell if the suspect was aligned with al Qaeda or localized Islamic organizations in Kosovo.
The U.S. military has long had concerns about anti-American, anti-NATO groups in Kosovo, where the force has a peacekeeping mission, a senior US military official told the Journal.
Federal prosecutors, who in Germany are responsible for "terrorist" cases, took over the inquiry Thursday.
German media said there were growing indications to suggest that Arid Uka is an Islamist extremist. Investigators were studying a page on social networking website Facebook believed to belong to the suspect, on which he made no secret of his extremist tendencies, Spiegel said. On the page he was a "fan" of several Islamic websites and had a link to a jihadi war song.
The attacker, whose father is an Imam, watched online videos of Islamic rappers and preachers, and divided the world into believers and non-believers, Welt newspaper reported quoting internet postings.
One of the videos he searched for was of Sheikh Abdellatif, a radical Moroccan cleric who was arrested Feb. 28 during a raid in Frankfurt, Spiegel reported. Police said the cleric and four other alleged recruiters were suspected of recruiting young men for terrorist training abroad.
The airmen had just flown to Frankfurt from the U.K. and were to be taken by bus to the US Ramstein Air Force base nearby. Around 10 to 15 U.S. personnel were on the bus when the gunman opened fire.
A military statement said on the dead servicemen was transiting through Germany en route to Afghanistan.
One of the victims was smoking a cigarette when the suspect pulled out a firearm and shot him, a German official told Fox News Channel. Another serviceman was gunned down as he returned a luggage trolley.
The attacker, reportedly wielding a knife and a handgun, then boarded the bus and fired at the driver before being taken down.
German police and an American serviceman tackled the suspect outside the vast airport's Terminal 2 building. He reportedly had a handgun and large amounts of ammunition in his possession, and tried to escape after his gun jammed.
President Barack Obama said he was saddened and outraged by the attack.
"We will spare no effort in learning how this outrageous act took place and working with German authorities to ensure that all of the perpetrators are brought to justice," he told reporters at the White House.
The incident came a month after German authorities had announced that additional security measures imposed late last year in response to indications of an imminent "terrorist" attack were set to be gradually scaled back.
The 9/11 attacks were partly planned German city of Hamburg by an al Qaeda cell led by Mohammed Atta, the hijacker of the first plane to strike New York's World Trade Center.