Robert "Bobby" Wilkes was a Petty Officer First Class who prior to being assigned to the USS Enterprise was an Emergency Medical Tech.
He suffered a meth overdose and was taken to the ship's sickbay where he received treatment for the overdose. Upon Special Agent Leroy Jethro Gibbs interviewing him, Wilkes insisted over and over again that he had never taken any drugs and was even convinced that none of his crew-mates had either. He even believed that the urine test that he had been given was a false positive.
Unfortunately, Wilkes fell into a coma and despite efforts to save him, died with his body being sent to NCIS where Medical Examiner Donald Mallard conducted an autopsy on him to find the cause of death.
Gibbs suspected that he had been murdered to stop him telling the Agents who his supplier was although Special Agent Stanley Burley suggested that Wilkes could have killed himself after receiving a call from his "very proud retired Chief Petty Officer father" due to the fact that Wilkes's prints were found on his saline bag.
Despite this, it remains unclear whether Wilkes was murdered or if his death was a suicide.