A pensioner has become the sixth person arrested in connection to the shooting of an off-duty senior police officer as he coached a junior football team in Northern Ireland.

Police are holding a 71-year-old man under the Terrorism Act after Detective Chief Inspector John Caldwell was shot four times in front of his traumatised son on Wednesday night.

Mr Caldwell, 48, remains in a critical condition. Hundreds of people today gathered in the streets to demand an end to the violence.

Detectives have publicly stated they believe the shooting is terror related and have linked the attack, which they're deeming attempted murder, to the dissident republican group the New IRA.

The latest suspect is now the sixth person to be arrested in connection to the shooting.

Police earlier revealed they'd been granted more time to question the initial four suspects, aged 22, 38, 45 and 47, until 10pm on Tuesday February 28.

A fifth man, aged 43, who was arrested on Friday, also remains in custody.

Members of the public who may have more information are still being urged to come forward. 

The local community rallied behind Mr Caldwell and his family, demanding an end to the violence on the streets of Omagh. 

On Saturday, the main street of Omagh was brought to a standstill by the protesters, who chanted and held posters which read: 'No going back.' 

The slogan refers to the history of violence and terror in Northern Ireland. The rally was organised by trade unions. 

Anton McCabe, secretary of Omagh Trade Union Council, said they were mindful a man remains critically ill, and children traumatised by the incident, and wanted to have a rally that was as respectful as possible. 

'We are here today to say no going back - no going back to violence, fear and injustices,' he told those gathered. 

Patricia McKeown of Unison said peace in Northern Ireland was only born when 'a massacre was perpetrated on the men, women and children of Omagh'. 

The protest took place a short distance from where a 1998 dissident republican bomb killed 29 people, including a woman pregnant with twins. 

'Twenty-five years later, the attempt has been made again and your spirit and resolve is not broken,' Ms McKeown said. 

'The factions who rejected our peace agreement will not change the resolve of the people.' 

Padraig Mulholland of Nipsa said there are two Omaghs. 

'There is the Omagh where this attack took place, but there is the positive Omagh; there is the Omagh that wants positive change and that was best represented by health and education workers who held another protest here earlier this week. They were here for young people, for working people, trying to fight for a better future,' he said. 

'No going back, let's fight for a better future for all.' 

Mr McCabe made the final address, saying: 'A clear message has gone out today: no going back. 

'Those who shot John Caldwell on Wednesday were in serious danger of lighting a fire that could burn us all, and let us be clear, the people of Omagh today have said no - no going back. 

'We are standing not just in horror at what was done to John Caldwell, but standing here saying, 'Let us build a better society, of justice, peace and equality'.' 

A minute's silence was observed. 

The high profile police officer, who has led a number of major investigations, cried 'I've been shot, I've been shot' before collapsing on a running track 30 yards from where he was attacked, as children ran in terror to get to safety.

Mr Caldwell was hit four times as he loaded footballs into his car, while his son, 12, 'came within a hair's breadth of being shot'. 

Speaking after the event, Mr McCabe hailed those who attended the rally, describing it as a strong message from the people of Northern Ireland that they do not want to return to violence. 

Earlier, hundreds gathered in Beragh, about eight miles from Omagh, for a walk of solidarity from the Beragh Swifts ground for Mr Caldwell. 

Beragh Swifts chairman Richard Lyons said the community gathered in support of their friend and for all the children affected by the shooting. 

'It's been a very difficult time for the club; it's been a very difficult time for the community,' he said. 

'John worked tirelessly for this club. He's no different to any other volunteer... the contribution that John gives to this club is phenomenal and this is an unbelievably difficult time for us all.'