Seoul-based rights group Transitional Justice Working Group (TJWG) released a report Wednesday on human rights abuses in North Korea. The report, titled “Mapping Killings under Kim Jong-un: North Korea’s Response to International Pressure” pulls information from six years of research and 683 escapee interviews to track killing sites, mass graves, and other locations which may contain evidence about human rights abuses.

TJWG concluded that North Korean authorities have changed their killing practices “in response to international criticism” and now select execution sites that are “easier to control,” such as locations away from the South Korean border and residential areas.

Of the 683 escapees, TJWG interviewed 537 women and 145 men. 200 interviewees lived in North Korea during Kim Jung-un’s ten-year reign. Most interviewees are between 40 and 80 years old.

The escapees described public executions under Kim Jong-un in fields, airfields, riverbanks and mountains with crowds that may have reached the thousands. However, according to one escapee, “in recent years, the viewing of the executions seemed to be reserved for groups affiliated with the organization the accused comes from,” like the accused’s coworkers or family.

TJWG collected evidence of four cases in which the accused was sentenced to death but not executed in public. The organization fears these cases may indicate a growing preference for secret executions.

Moving forward, TJWG will collect firsthand accounts of private executions, attempt to “identify those responsible for authorizing violence against citizens” and work to track locations of “possible repositories of documents that may contain evidence” of human rights violations.