The elder brother of Foyzur Rahman fled with Foyzur's mobile phone and tab soon after the attack on Prof Dr Zafar Iqbal was carried out, counterterrorism officials said.
Law enforcers are looking for the devices as they believe they could track Foyzur's communication records analysing those gadgets.
“Foyzur left his phone and tab in his house before going to the campus for the attack. His brother Enamul Hasan fled with the devices soon after the attack,” an official of the Counter Terrorism and Transnational Crime Unit told The Daily Star yesterday.
“He might have used different encrypted mobile applications to communicate with others,” he added.
Police have been looking for his cellphone since he was detained on Shahjalal University of Science and Technology (SUST) campus after the attack on Saturday.
Contacted, Saiful Islam, additional deputy commissioner of CTTC, said they are trying to trace Enamul as it is very necessary to recover the evidence.
The police also believe Enamul was aware of the attack and Foyzur's involvement with militant groups.
The law enforcers had earlier seized a CPU from the house of Foyzur's uncle Fozlur Rahman. It is believed the attacker was using the computer, which is under examination now.
Foyzur claims he has been self-radicalised and got involved in extremism online in 2016. He started taking the final preparation for the attack one and a half months ago, the police said.
According to the police, at least four suspects were present near the campus just a day before the attack.
The law enforcers suspect the attacker was in touch with banned militant outfit Ansar al Islam as the attack bears the hallmark of the other attacks carried out by the militant group.
Dr Iqbal, a faculty member of computer science and engineering at SUST, came under the knife attack from behind during a programme on the campus on Saturday.
Police with the support of students and locals arrested Foyzur and recovered a knife and a bicycle key from his possession.
He was seen in the CCTV footage entering the campus riding the bicycle, which was recovered from a garage near the campus later. Law enforcers are also trying to find out how it reached the garage.
Foyzur used to live in Sylhet city with his parents but sometimes went traceless for several days. His parents who went into hiding following the murder attempt surrendered to the police on Monday.
His parents told the police Foyzur, a follower of Salafism, did not maintain good relations with his father but with his two uncles living in Kuwait. Police suspect he embraced Salafism influenced by his uncles.
Our Sylhet Correspondent visited Foyzur's village home at Koliarkapon under Dirai upazila in Sunamganj yesterday. Locals said Foyzur used to sell clothes during his visit to the village.
“He sold clothes in the local market last year and was seen selling clothes for the last time three months ago,” Foyzur's uncle Abdul Kahhar told The Daily Star. He used to sell clothes only in the afternoon, he added.
Earlier, police in Rajshahi claimed to have found militants running their activities in guise of selling clothes in the area.
Abdul Wahab Mia, additional deputy commissioner of Sylhet Metropolitan Police, said they would investigate the reason behind selling clothes during Foyzur's short visit to his native village.
DR IQBAL SHIFTED TO CABIN
Dr Iqbal, who is receiving treatment at the Combined Military Hospital in the capital, was shifted to a cabin from the intensive care unit yesterday afternoon as his condition improved, said Maj Gen Munshi Md Mojibur Rahman, chief cardiac surgeon and consultant surgeon general of Bangladesh Armed Forces.
He added Zafar was not facing any difficulties and was himself taking meals and even going to the washroom without assistance. He also read books and newspapers and resumed his writings, Mojibur said.
It will take seven to eight days to remove the stitches from his wound, they informed.