Rwanda Investigation Bureau (RIB) on Friday paraded FLN Spokesperson 'Captain' Herman Nsengimana, who it said is being investigated over terrorism charges, including murder and forming an illegal armed group, among others.
Nsengimana was among the 291 militia fighters from Conseil national pour la renaissance et la démocratie (CNRD) who were handed over to Rwanda by Congolese authorities last month after being captured by the Congolese army (FARDC) in South Kivu Province.
The FLN is the armed wing of CNRD.
He was paraded before the media at RIB headquarters along with Théobard Mutarambirwa, the Secretary General of a faction of PS Imberakuri, who was also captured with him in DR Congo and brought to Rwanda last month.
Mutarambirwa is from the Imberakuri faction headed by Bernard Ntaganda.
RIB Spokesperson Marie-Michelle Umuhoza said: "We received them today (Friday) and are now going to start working on their case files."
Both men - former teachers in different secondary schools in the country - are terror suspects.
Nsengimana was a teacher at GS Rwanamizo in Nyanza District, Southern Province while Mutarambirwa was teaching at Ecole Technique Muhazi (ETM) in Kigali.
Last year, more than 2,000 fighters of the CNRD militia group and their dependants were captured by the Congolese army during the ongoing military offensive in the high plateaus of Kalehe territory, in South Kivu Province.
This is where the CNRD - part of the larger MRCD-Ubumwe political platform led by Belgium-based former Rwandan Prime Minister Faustin Twagiramungu, and Paul Rusesabagina, was entrenched.
Umuhoza said: "We would like to urge Rwandans not to be duped by such criminals into joining such negative groups intent on destroying all the good things this country has achieved. Rwandans should continue playing a vital role in reporting people with such intentions whenever they hear about them."
The 2018 law on counter terrorism stipulates that such crimes can be investigated for 15 days at RIB before case files are submitted to prosecution.
However, that time period can be extended to 90 days when approved by the prosecutor given the gravity or nature of the case.
The Congolese army has stepped up its offensive against anti-Kigali terror groups in an ongoing effort to rout all foreign armed militias based there.
The CNRD is one of the groups that split from FDLR, an offshoot of the forces and militia groups that crossed into DR Congo from Rwanda after killing more than a million people during the 1994 Genocide against the Tutsi in Rwanda, in 2016.
Nsengimana was appointed the terrorist outfit's mouthpiece earlier last year after his predecessor, Callixte Nsabimana, was apprehended - he is currently in custody in Rwanda.
Late last year, the most senior among those brought home was Gatabazi, alias Gatos Avemaria, who was the militia's head of military operations.
The RIB spokesperson told reporters that no criminal will evade justice as all will be brought to book soon or later.
"It is a process that is ongoing and all will be investigated and charged accordingly."
Last year, Congolese President Félix Tshisekedi vowed to deal with the problem of insecurity in his country's restless east where a myriad of militia - local and foreign - have wreaked havoc for decades.
Among others, last September, the Congolese army killed the former supreme commander of the genocidal militia FDLR Sylvestre Mudacumura, who had evaded capture for over a decade.