An assistant regional transport officer (ARTO) of Barasat was arrested on Wednesday for tampering with documents and issuing fake registration numbers to allow vehicles registered outside Bengal to ply in the state.

Three more officials of the department, two of them seniors, also face probe based on a complaint filed by North 24-Parganas district magistrate Sanjay Bansal.

The FIR Bansal filed with Barasat police station names regional transport officers (RTO), Prabudhha Dasgupta and Ranjan Sen and ARTOs Souren Das and Samir Ranjan Pramanik.

Pramanik was arrested on Wednesday before being admitted to hospital on health grounds.

According to transport department sources, a software named Vahan is used to maintain all data related to registration of vehicles across the state. This software ensures that no two vehicles with same chassis or engine number can be registered. This ensures that no two vehicles have the same registration number across regional transport offices.

But Pramanik and the rest possibly found a way to tamper with the software.

Sources said Bansal received a complaint of corruption against the four transport officials.

“It was also mentioned in the letter how these officers were issuing vehicle registration numbers same as those issued by the transport department in Odisha,” an officer said.

“There were some specific tip-offs about malpractices by the accused officers. Since the district magistrate oversees the functions of the regional transport offices in the districts, Bansal inquired into the veracity of the complaints secretly and came to know that the allegations were true,” said an official of the district magistrate’s office.

Police suspect that other transport officials may also be involved in the racket. “There must be juniors who were aware of the malpractice,” said an officer investigating the case. “This is an organised racket. We found that owners of vehicles that carry goods offer money to transport officials to get registration numbers.”

“Investigation led police to seize five oil tankers from Howrah on Thursday and arrest the owners of four,” the North 24-Parganas superintendent of police, Champak Bhattacharya, said.

The owner of one of the seized oil tankers confessed that he had been issued the fake documents by the regional transport office in Barasat.

“We suspect the accused official has already issued several documents against fake registration numbers. The other three officials are being examined thoroughly and we expect to track down several vehicles with fake registration numbers soon,” an officer of Barasat police station said.