Kim Jong Nam didn’t have a heart attack and the medics who conducted his autopsy found no obvious puncture marks or wounds, a top Malaysian health official said Tuesday, compounding the mystery over the North Korean’s death.

Dr. Noor Hisham Abdullah, the director-general of Malaysia’s Ministry of Health, addressed a packed room of journalists at the morgue where Kim’s body is being held, saying that the cause of death won’t be released until lab tests from the autopsy are completed.

Authorities in South Korea believe that Kim, the older, estranged half-brother of North Korean leader Kim Jong Un, was poisoned before he died on February 13. His death is being investigated as murder.

When asked about reports that Kim had been poisoned, Abdullah reiterated that his department was waiting on lab results before making any conclusive statements.