- Police said nine men and two women, aged between 21 and 72, were detained under the Terrorism Act on Friday morning.
- The shooting, which happened in front of school children, was widely condemned by political figures across Northern Ireland and beyond.
Eleven people have been arrested in County Tyrone over the attempted murder of senior detective John Caldwell.
Police have also released new CCTV footage and photographs of vehicles they believe were used in the attack.
Det Ch Insp Caldwell was shot while putting footballs into his car at a sports complex in Omagh on 22 February.
Police said nine men and two women, aged between 21 and 72, were detained under the Terrorism Act on Friday morning.
Det Ch Supt Eamonn Corrigan said the search and arrest operation in Omagh and Coalisland in County Tyrone marked a "significant development" in the investigation.
The shooting, which happened in front of school children, was widely condemned by political figures across Northern Ireland and beyond.
On Friday, police said three vehicles they believed were used by the gunmen were spotted travelling in convoy on the Drumnakilly Road in the direction of Omagh in the hours before the attack.
Seven of those arrested on Friday had been previously detained in relation to the shooting, Mr Corrigan added.
Det Ch Insp Caldwell was discharged from hospital in April and police said he had since given his account of events to investigators.
He was visited by Prime Minister Rishi Sunak during his treatment and on Wednesday met King Charles ahead of his first public appearance since the shooting at Hillsborough Castle.
"I am delighted that John is on the road to recovery and was able to attend a garden party this week hosted by the King and Queen," Det Ch Supt Eamonn Corrigan said.
"Now we have to make sure we bring those vile individuals who tried to murder him to justice.
Officers believe the dissident republican group the New IRA may have acted with an organised crime gang to carry out the attack, which left the detective chief inspector with life-changing injuries.
Twenty-one people have been arrested and questioned in total since the beginning of the investigation.
No-one has been charged.
Police have previously said two Ford Fiesta cars they believe were used in the attack had been bought in Ballyclare and Glengormley in County Antrim in the weeks before the attack.
They were later found destroyed after the shooting.
Detectives have since identified a third vehicle, a black Mercedes Benz C-Class, which they believed was used as an operational vehicle both before and immediately after the attack.
Newly released CCTV footage shows all three vehicles in convoy on the Drumnakilly Road in the direction of Omagh in the hours before the attack.
Detectives have said an estimated 400,000 hours of CCTV footage has been seized for analysis in the hunt for those involved in the shooting.
Who is detective John Caldwell?
He is one of the best-known detectives in the Police Service of Northern Ireland, often fronting press conferences on major inquiries during his 26-year career.
Mr Caldwell investigated the 2011 murder of his colleague Ronan Kerr by dissident republicans.
He was aware his investigations relating to dissident republican attacks - including the killing of Lyra McKee in 2019 - made him a high-profile target.
In January, he spoke to reporters after the killing of Shane Whitla, a 39-year-old father of four who was shot a number of times in the town of Lurgan in County Armagh.
He was also the initial lead detective investigating the killing of Natalie McNally in Lurgan, and he was involved in investigating the murder of Mark Lovell, 58, who was shot a number of times at close range in his car in Newry in County Down on 1 December.
He had received a number of threats in the past, BBC News NI understands.