With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: On numerous occasions in the past, especially, during military regime, security forces and police have arrested and detained journalists who criticized the government. Reporting on matters such as political corruption and security issues are particularly sensitive. Politicians and political parties harass journalists perceived as reporting on them or their interests in a negative manner. During local and state elections, journalists have been intimidated for covering certain election-related events. The militant group Boko Haram threatens media outlets and has killed members of the press. On 20 January 2012, Channels TV reporter Enenche Akogwu was reporting on the Boko Haram attacks and bombings in Kano that day when he was killed by gunmen whose identities remain a mystery. Journalists practice self-censorship.
text_B: Was enough information about the killers revealed at the time for authorities to know if they were responsible for any prior murders?
NO.