It looks like the North Koreans may have been sending a message to the ROK Defense Minister who is a frequent target of North Korean propaganda and vitrol:
SEOUL, April 23 (Yonhap) — A suspicious white powder sent to the South Korean defense minister on Tuesday turned out to be wheat flour and an investigation was underway to determine who was behind the act, military officials said.
Earlier in the day, Defense Minister Kim Kwan-jin received a parcel containing a threatening letter and white powder, in what the ministry called “an attempted act of terrorism” against the defense chief.
The parcel, which was sent days after hundreds of leaflets threatening Kim were distributed near the ministry building, sparked security concerns for military leaders who have pledged to sternly respond to any provocations from North Korea. [Yonhap]
You can read more at the link, but the North Koreans could be trying to regain the news cycle in South Korea with this incident. The North Koreans likely will not do anything to try and recapture the US media’s attention until the non-stop coverage of the Boston Marathon Bombing dies down.