Detective Chief Inspector John Caldwell remains critically ill after the attack in Co Tyrone on Wednesday night in which he was shot in front of his young son.
He was targeted at a sports centre where he coaches a youth football team and police believe the two gunmen involved fired multiple shots.
The Police Service of Northern Ireland (PSNI) said on Saturday night that they have arrested a 71-year-old man in Omagh under the Terrorism Act.
The man, the sixth to be arrested in the investigation, will be questioned by detectives at Musgrave Serious Crime Suite.
Five other men – aged 22, 38, 43, 45 and 47 – also arrested in connection with the attempted murder remain in custody.
Earlier on Saturday, the PSNI said they had been granted more time to question four of the men.
A PSNI spokesperson said a court in Belfast had granted an extension to the detention of four male suspects, aged 22, 38, 45 and 47, until 10pm on Tuesday February 28.
Police have said dissident republican group the New IRA is their primary line of inquiry.
Meanwhile, hundreds of people gathered to demand an end to paramilitary violence in Northern Ireland.
The main street of Omagh was brought to a standstill on Saturday as crowds assembled in front of the courthouse for a rally in solidarity with Mr Caldwell.
Standing a short distance from where a 1998 dissident republican bomb killed 29 people, including a woman pregnant with twins, they held posters saying: “No going back.”
Earlier, Beragh Swifts, the football club at which Mr Caldwell is a volunteer coach, led a solidarity walk through the village of Beragh on the outskirts of Omagh.
