Alaa Albakr told Reuters by phone that his brother said he went to Syria to volunteer with emergency rescue workers, but Alaa believes he was radicalized by imams in Berlin who "brainwashed him" into returning to his country for jihad.

"This is why we believe he returned to Syria," Alaa told Reuters by phone from the village of Sa'sa' southwest of Damascus.

"He went to Turkey seven months ago and spent two months in Syria. He called us and told us 'I'm volunteering with the White Helmets (emergency teams) in Idlib'."

Pressed to say if his brother had joined Islamist militant groups in Syria, Alaa Albakr said he could neither confirm nor deny if that was the case.

Idlib, a city near the border with Turkey, and the province by the same name, is a stronghold of rebel groups including Jabhat Fateh al-Sham, formerly the al Qaeda-linked Nusra Front.

Alaa said Jaber, who had refugee status in Germany and committed suicide after being arrested on suspicion of planning a bomb attack at a Berlin airport, was a devout Muslim who had wanted to attend university.

Reuters was able to identify Alaa Albakr through a picture he posted on Facebook showing his brother posing in front of a row of houses in what is clearly Germany, along with a brief obituary.

Jaber Albakr had a Facebook account under the nickname Jaber Abou Hayyan. The brothers' accounts are linked.

RADICALIZATION

Alaa said his brother started showing signs of radicalization late last year. Until then, he would never have thought of carrying out an attack in Germany, Alaa said.

"Last year he started posting jihadi videos and songs," he said. However he said he did not understand why his brother would have wanted to attack a country which had helped him and thousands of other Syrians, when he could have targeted soldiers loyal to President Bashar al-Assad in Syria.

"Unfortunately we have lost all feelings here in Syria. We only believe in logic. And this doesn't make sense."

On February 26, Jaber Albakr posted a video on Facebook showing dozens of Islamic state fighters at an unknown location singing jihadi songs and vowing to advance on the Yemeni capital Sana'a.

A month earlier he wrote on Facebook: "Mother don't be sad. I'm going to Iraqi lands. Wipe the tears off your eyes. I'm going to expel the Jews."

But Alaa said that despite the Facebook postings, he showed no sign of intent to commit acts of violence during a phone conversation several weeks before his arrest on Monday.

"He called me six weeks ago to tell me that he wanted to finish his studies," he said. "He tried to convince me to bring my wife and five children to Germany."

Jaber, 22, evaded a police raid at his apartment in Chemnitz where explosives were found, but was handed over to police by fellow Syrian refugees who tied him up in their flat in Leipzig where they had sheltered him after he asked for help.

"I was relieved when I read that he was arrested ... I thought he is safe now and he will be proven innocent," he said, sounding angry, and then sobbing. "He was a devout Muslim and devout Muslims don't commit suicide."

Alaa sent Reuters pictures showing his brother smiling while cycling or posing in a sombrero hat next to a river in Germany.

HAUNTED BY FRIEND'S DEATH

But his online postings also revealed torment. Last year, Jaber posted a picture of his best friend Maysara, who died in a government prison in 2014, with the caption: "Brother, you have been waiting too long for me. I'm coming to you soon."

Another school friend from the same village as the brothers, who now lives in Germany, said Maysara's death affected Jaber deeply. But he was still surprised by news of Jaber's arrest.

"I remember him as a gentle and honorable young man," the 24-year-old friend said by phone from the northern German city of Bremen. He asked to be referred to by his nickname, Abdo al-Majeed, fearing for his own safety and for his family in Syria.

Majeed came to Germany in mid-2015, a few months after Jaber. "He and his family are well respected throughout the village. I could not believe it when I read about his arrest online," said Majeed, who last spoke to Jaber a year ago by phone in Germany.

"He called me to ask how I was doing. He sounded like the same Jaber I knew from school: gentle and caring."

Like Jaber's brother, he said he and a dozen fellow Syrian refugees in Bremen believe Jaber must have been radicalized in Germany.

"The situation in Syria is so bad, it is a nightmare. I have no idea why someone would want to return," he said.

"If he indeed had returned (to Syria), it indicates that someone here in Germany had brainwashed him and convinced him it was the right thing to do," Majeed added.