The report said that the men had driven their vehicle into the police yard before getting out to stage the attack.
The attack is the latest in a spate of attacks in the country.
It is said to be the deadliest since the 2002 Bali attack.
A number of terrorist attacks have occurred in Indonesia in recent days targeting churches and police stations.
Indonesian media said one attacker may have had a bomb strapped to his body but police did not immediately confirm the reports.
No group has taken responsibility so far.
The police earlier disclosed that 8 militants with a white minivan launched the attacks. On Sunday a radicalized family carried out three suicide bombings on Christian churches in the East Java city of Surabaya, claiming ten lives and injuring over 40 other people.
All six bombers were killed, including the mother who was Indonesia's first known female suicide bomber.
State news agency Antara said two journalists who had been at the police headquarters were also hurt in the attack.
Police have been frequent targets of mostly low level attacks by local militants, including a 2017 suicide bombing at a bus station in Jakarta that killed three police officers.
The families have been linked to the local chapter of Indonesian extremist network Jamaah Ansharut Daulah (JAD), which police said was behind the attacks.
Setyo said one of the assailants was captured and taken to the Pekanbaru Police station for interrogation.
They followed a deadly prison riot staged by Islamist prisoners at a high-security jail near Jakarta last week.