Firdaus, who fought alongside Sofjan during their student days in 1966 to bring down President Sukarno, said he did not think Sofjan was capable of defying the police.
"I know Sofjan very well. We go back a long way to our days as student activists in 1966," he told The Jakarta Post.
"He is such a consistent person, who will always keep his words and promises. I'm sure he will be home as soon as he completes his business affairs abroad," he added.
Cosmas Batubara, a former cabinet minister and fellow student activist, also vouched for Sofjan's integrity yesterday.
"He's not likely to flee the country. He's very loyal to the nation," Cosmas said.
"I know he travels abroad a lot, but he does it for good reasons. If they (the authorities) needed him for questioning, they should just call him ... He will return."
Sources close to Sofjan said yesterday that he would return from Australia this weekend.
Sofjan was questioned by the military last month in connection with a bombing in Jakarta which the authorities said was perpetrated by the outlawed Democratic People's Party (PRD).
The chairman of Gemala group was mentioned as a potential financier in one of the documents found in the Jakarta apartment where the home-mad bomb exploded on Jan. 18.
Sofjan has denied any link with PRD, but he drew criticism from the military by leaving for Australia last week.
Armed Forces chief Gen. Feisal Tanjung has said that while Sofjan had not been barred from traveling abroad, he should stay in the country in case the authorities needed him in connection with the bombing investigation.
Firdaus, like Sofjan, was a member of the Front for Students Action which organized street protests that led to Sukarno's downfall and ushered in the New Order administration of President Soeharto in 1966.
Several other former student leaders from that era including three now serving in the cabinet have also attested to Sofjan's integrity and character, and expressed the opinion that he was unlikely to betray the New Order which he helped establish.
Jakarta Police Chief Maj. Gen. Hamami Nata said yesterday that Sofjan would be questioned again soon.
Hamami did not give an exact date but sources close to Sofjan said that he had been summoned by the police for questioning as a witness in the bombing investigation next Tuesday.
Minister of Justice Oetojo Oesman said yesterday his office had not received any request to ban Sofjan from leaving the country.
The ministry, which oversees the Directorate General of Immigration, had not received any request to slap a travel ban on Sofjan either, Oetojo said.
The decision to issue a travel ban would depend on the bombing investigation, he said. (imn/byg/cst)