The man, aged 22 years old was arrested in the Coalisland area under Section 41 the Terrorism Act in the early hours of Friday morning.
He is currently being questioned by detectives from the PSNI’s Major Investigation Team at Musgrave Serious Crime Suite.
Three men aged 38, 45 and 47 years old arrested on Thursday morning in connection with the attempted murder remain in police custody at this time.
DCI Caldwell was shot multiple times on Wednesday, February 22, outside a sports complex at the Killyclogher Road area of Omagh have this morning, Friday 24th February, made a fourth arrest.
He was putting footballs into the boot of his car when two masked men came out of the shadows and shot him several times.
DCI Caldwell managed to run away for a short distance but feel to the ground. The gunmen pursued him and fired into him again.
He was rushed to the emergency department at Altnagelvin Hospital in Derry where he underwent surgery for his injuries.
Police chiefs say he is critical but stable and is fighting for his life.Tags: