Australian Federal Police believe 29-year-old Abraham Succarieh is fighting for terror group Jabhat al-Nusra, following in the footsteps of his "martyred" brother Ahmed.

A third Succarieh brother, Omar, was charged last week with funding Jabhat al-Nusra and planning to travel to Syria "for the purpose of engaging in hostile activities".

Details about Abraham's alleged involvement with the al-Qaeda-linked group were revealed in an AFP affidavit tendered to court during Omar's bail application in Brisbane this week.

"Abraham departed Australia on 10 September 2013 and it is reasonably believed that he is conducting military activities leading a group of militants fighting for specified terrorist organisation Jabahat Al Nusra [sic] (JN) in Syria," the affidavit states.

Authorities believe Abraham flew out of Brisbane on Emirates flight EK144 to Dubai, the day before Ahmed detonated a bomb in the Syrian city of Deir al Zor.

Ahmed reportedly went by the alias Abu Asma al-Australi while in Syria. He was allegedly the man filmed reciting a passage from the Koran and delivering a call to arms for Muslims to rise up. The video cuts and resumes showing a huge explosion in the distance.

"Subsequent enquiries identified that the suicide bomber responsible for this attack was Ahmed Succarieh," the police affidavit states.

Police allege Brisbane-based Omar secretly began sending money to his other brother Abraham and fellow Syrian Jabhat al-Nusra members in 2014.

An alleged transfer in June was for $27,000 and there was another alleged transfer four months earlier, however police were not sure how much was sent.

Police claimed the money passed from Omar to Abraham, via an unknown courier in Lebanon, Omar's brother-in-law, his wife Razan, his mother Fatima and another unknown intermediary.

Between April 29 and June 27, police say phone intercepts captured the brothers speaking in code about the money when they referred to "30 kilos of sweets" and converting amounts of "Aussie" and "US".

Police also claimed a recording device placed inside the Islamic book store Omar owned in Underwood, which captured him speaking over the phone with another man in Syria.

The man reportedly told Omar he needed "about $2600 a month", to which Omar replied, "going to try my best to organise, ah, maybe like one year's worth. About twenty, thirty grand."

Another recording from inside the iQraa Islamic Centre also purportedly captured Omar talking about the price of a "wedding" in Sydney.

"I reckon all up that probably cost fifteen grand. So do you know how many bullets 15 grand is," Omar allegedly said.

Police then claim Omar says the money would have purchased 10,000 bullets for an AK-47 rifle.

Omar was also allegedly captured talking about Jabhat al-Nusra execution videos and stating "I love Jahbat al-Nusra".