The 75-year-old actor was arrested in Upper Iweka Bridge in Onitsha, Anambra State.
Agu, who was carrying a charity activity, was picked up by soldiers for wearing a Biafra themed outfit.
He was, however, released, but DSS rearrested him.
Following his rearrest, DSS was said to have flown him to Abuja for further interrogation.
DSS released him following intervention of Actors Guild of Nigeria, AGN.
Speaking on his release, activist lawyer, Mike Ozekhome said DSS released Agu after they searching his phone and found nothing incriminating.
Narrating his experience while in detention, Agu said no security operatives “touched” him.
Agu disclosed this at Enugu on Thursday during a welcome back event organized by AGN members.
The veteran actor said most of the security agents tried to familiarize themselves with him while in detention.
“It didn’t start well but God took control. I was only buying bread for the poor. Soldiers came in and started scattering things. They said they are calling me in the office but they did not tell me my offence. Because they did not tell me my offence, I refused to follow them.
“That drama that took place was important so that they will know that Igbo are here. That moment of Upper Iweka till the time we got to the army barracks close to Zik Mausoleum, to 82 Division of the Nigerian Army and to DSS office in Abuja, nobody touched me. They treated me with respect.
“Every officer wanted to be involved in the case so that they can have opportunity to interact with Chinwetalu Agu.”