KUALA LUMPUR, Malaysia—Malaysian police said one of the suspects in the killing of Kim Jong Nam, the older half brother of dictator Kim Jong Un, works at the North Korean embassy in Kuala Lumpur and Malaysia has sought custody of seven suspects.

Hyon Kwang Song, 44 years old, is a second secretary in the North Korean embassy in Kuala Lumpur while another suspect, Kim Uk Il, works for state-owned airline Air Koryo, Malaysia’s Director General of Police Khalid Abu Bakar said at a press conference Wednesday.

North Korea’s embassy in Kuala Lumpur didn’t accept calls seeking comment.

Mr. Khalid also said security has been tightened around the morgue where Mr. Kim’s body is being kept following an attempt to break into the building.

Malaysia declined a North Korean offer to conduct a joint investigation into the Feb. 13 killing and has asked the local embassy to hand over the suspects, four of whom are believed to have returned to Pyongyang, Mr. Khalid said.

Mr. Kim was attacked by two women at Kuala Lumpur International Airport as he was waiting to check in for a flight to Macau. The two female suspects, who are in police custody, were trained to carry out the killing, which is at odds with their claim that they believed they were playing a prank. They rehearsed the operation in at least two malls in Kuala Lumpur, Mr. Khalid said.

Police in Malaysia were seeking Wednesday to extend the custody of the two women and a North Korean suspect arrested last week. However, a suspect from Malaysia will be released, the police chief said.

Results from laboratory reports on Mr. Kim’s body after a Feb. 15 post mortem are still outstanding and no family member has turned up to either claim the body or provide samples for a DNA test, the police chief said.

Malaysia has requested that North Korea produce the family of Mr. Kim for DNA matching and to claim the body.