The officer was arrested on Wednesday night and was being interrogated by detectives from the CID and Anti-Terrorism Police Unit, police said.
A senior police officer in Garissa told Capital News that the ex-officer was arrested at a hotel after the parent of a 14-year-old boy who had undergone training was rescued from him.
“There have been reports of involvement of an Administration Police officer, now we know who he is. He has been arrested and will face relevant charges,” the senior officer said speaking on condition of anonymity.
He said the boy who was rescued from a training centre had recorded a statement with the police, which he described as “vital in our investigations.”
“There is a lot which has been revealed; the boy is helping us and I am sure we will get more people who had been trained by the former AP officer,” the officer added.
North Eastern Provincial Police chief Leo Nyongesa confirmed the arrest but he did not divulge more details.
“The man is under interrogation… there is little we can say at the moment,” Nyongesa said.
Police believe the officer was instrumental in grenade and other explosive attacks that have rocked the region since October last year when Al Shabaab vowed retaliation attacks on security forces to protest a military incursion targeting them in their country.
On Thursday, four police officers escaped death narrowly in Mandera following a major explosion in the town.
A vehicle carrying police officers had just passed when an improvised bomb went off, causing an explosion.
“There has been an explosion, but no one was injured,” a senior police officer said.
In the last quarter of last year, at least 10 people were killed and dozens wounded in separate explosions reported in Mandera.
In one of the incidents, six people were killed on October 21when a bus they were travelling in was blown up by a grenade launched by people believed to have links with Al Shabaab militiamen.
Four people, including a police officer and a teacher were also killed in October while transporting examination materials.
On November 24, a soldier was killed and others wounded in a landmine attack on their vehicle in the border town. Barely two weeks later on December 12, an Administration Police officer was killed in another landmine attack.
Police blamed all the incidents on the notorious Al Shabaab militiamen who have vowed reprisal attacks to protest a military crackdown on their members by the Kenya military in Somalia.
Kenya Defence Forces crossed the border into Somalia in mid October after they because notorious of kidnappings of both locals and foreigners.
The militiamen had been blamed for the kidnapping of two foreign women from Lamu Island, including Frenchwoman Marie Dedieu who died while in captivity in Somalia.
They had also kidnapped two foreign aid workers from Dadaab refugee camp late last year before another kidnapping of a District Officer and an immigration officer from an Administration camp in Wajir. Both of them are still being held in Somalia.