Forensic experts have identified six American soldiers killed during the Korean War from 55 boxes of human remains returned by North Korea last year after the first summit between dictator Kim Jong-un and U.S. President Donald Trump.

The effort to recover American remains was suspended after the second Trump-Kim summit in Hanoi, Vietnam, ended on a more sour note in February.

“We have reached the point where we can no longer effectively plan, coordinate, and conduct field operations in the DPRK [North Korea] during this fiscal year, which ends on September 30, 2019,” the U.S. Defense POW/MIA Account Agency (DPAA) stated in early May.

Among the problems cited by DPAA was North Korea’s failure to negotiate details of the payments required by the North Korean military for supporting recovery efforts.

Military families expressed disappointment with the stalled recovery effort on Memorial Day, describing the situation as an emotional roller-coaster ride to Military.com. The families criticized Pyongyang for using what should be a purely humanitarian cooperative effort as a diplomatic bargaining chip and urged U.S. officials to reinforce their commitment to bringing every last soldier home.

According to the DPAA, some 5,300 American soldiers lost in the Korean War remain unaccounted for.

The remains are being examined by forensic anthropologists at a secure facility in Joint Base Pearl Harbor-Hickam. Acting Defense Secretary Patrick Shanahan visited the facility this week and praised the efforts of DPAA personnel.

Voice of America News reported on Wednesday that four families have been notified of the recovery of remains, while the other two families are awaiting notification. It is customary for authorities not to release names to the public before their families hear the news.

The Pentagon publicly identified one of the recovered soldiers on Wednesday as Army Cpl. Charles S. Lawler of Company M, 3rd Battalion, 8th Cavalry Regiment, 1st Cavalry Division. Lawler was reported missing in action on November 2, 1950, while fighting enemy forces near Unsan in North Korea.

The other three troops previously identified from the latest batch of remains were Army Master Sgt. Charles H. McDaniel, Amery Pfc. William H. Jones, and Army Sgt. Frank Julius Suliman.