Half slumped against the church wall as her son’s funeral plays out inside, Kavira Mwenge says in whisper, “I have so much anger in my heart. Who killed him?”

Justin, a 41-year-old police officer, was shot in the head by rebels as he stood guard outside an Ebola treatment unit in Butembo, eastern Congo, on March 7th. Nobody knows who was behind the attack.

Congo’s most volatile and dangerous province, which is home to more than a hundred rebel groups, is now hosting the second largest Ebola outbreak in history. On Monday, it was announced that 1,000 people have been infected with the virus since the start of August, and 621 have died.

Progress in stamping the disease out has been hampered by numerous cases of violence. Three recent attacks on treatment centres have been blamed on “Mai Mai rebels,” which means little as many groups that prowl the area take this name.

One centre, which was co-run by Médecins Sans Frontières (MSF), was burned to the ground on February 24. Its charred remains have since been abandoned. Just three days later, rebels charged into the second centre where MSF were working, waving machetes and guns.