The unknown attackers ransacked the apartment in Potiskum, Yobe state, after killing the doctors in the early hours.
It was unclear who carried out the killings. Potiskum has been frequently targeted by Islamist sect Boko Haram, a group that killed hundreds last year in its effort to carve out an Islamic state in Nigeria's mostly Muslim north.
However, there could also be a criminal motive as foreign workers are associated with wealth in Nigeria. Western embassies have designated northeastern states "red zones" and advise their nationals not to travel there.
Boko Haram's insurgency has contributed to a breakdown in order across the north of Africa's most populous nation and security sources believe criminal gangs carry out deadly armed robberies hoping the militants will be blamed.
"The three North Koreans were slaughtered at about 1 a.m.. They worked at the General Hospital," Yobe Police Commissioner Sanusi Rufai told Reuters by telephone.
The commissioner said in 2009 the reclusive state had struck an agreement with Yobe to send 18 doctors to different parts of the state.
This story has taught me something: When I saw the first report I automatically assumed that it was inspired by terrorism, that healthcare workers were the new target. I also assumed that the doctors must be South Korean, because...well, because who ever heard of North Koreans in Nigeria?
Even when I linked to the KBS World story that clearly said they were North Koreans, I didn't read closely enough to notice that fact right in the headline.
I was trying to fit surprising new information into an existing story—a story about Boko Haram, like their Pakistani counterparts, threatening health workers. So I started jumping to conclusions instead of waiting for more information. I'll try to do better.