Detective Superintendent John Caldwell remains seriously ill following the attack Fellow Tyron on Wednesday night in which he was shot in front of his young son.
He was targeting a sports center where he coaches a youth soccer team and police believe the two gunmen involved fired multiple shots.
Police of Northern Ireland (PSNI) said on Saturday night they have arrested a 71-year-old man in Omagh under the Terrorism Act.
The man, the sixth arrested in the investigation, will be questioned by detectives from the Musgrave Serious Crime Suite.
Five other men – ages 22, 38, 43, 45 and 47 – who were also arrested in connection with the attempted murder remain in custody.
Earlier on Saturday, the PSNI said they had been given more time to question four of the men.
A PSNI spokesman said a Belfast court has extended the detention of four male suspects aged 22, 38, 45 and 47 until 10pm on Tuesday 28 February.
The police have said the dissident republican group the New IRA is their primary line of research.
Meanwhile, hundreds of people rallied to demand an end to paramilitary violence in Northern Ireland.
Omagh’s high street was brought to a standstill on Saturday as crowds gathered outside the courthouse for a rally in solidarity with Mr Caldwell.
They stood a short distance from the site where a dissident Republican bomb killed 29 people in 1998, including a woman pregnant with twins. They held posters that read, “No turning back.”
Earlier, Beragh Swifts, the football club where Caldwell is a volunteer coach, led a solidarity walk through the village of Beragh on the outskirts of Omagh.