The desire for revenge against Nigeria’s heavy-handed military is a leading reason that people join the Boko Haram Islamic extremist group, according to a new study published Monday.

Nearly 60 percent of 119 former Boko Haram fighters interviewed in rehabilitation camps in the country’s northeast cited revenge against the military as having a strong, or being the only, influence in their recruitment.

“They kill innocent people that are not (Boko Haram) members … I think they deliberately do so. So they (victims) join the group to fight the military,” the study quoted one former extremist as saying.

The study also found that many interviewed said they were pressured into joining the extremists.