The white women's garment – which still had its $3.99 price tag attached – was not seized as evidence by police officers investigating the singer's death, despite legal experts speculating that it may have been used to mop up the singer's blood.
Top US attorney Craig Silverman – who is not involved with the investigation – said: "It's pretty extraordinary that a bloody shirt would not have been taken as evidence."
A Los Angeles police spokesperson refused to say why the garment hadn't been taken as possible evidence.
The spokesperson said: "I don't know why it wasn't taken. Our detectives aren't speaking about the investigation so we won't have an answer at the moment. I don't foresee one for some time."
Jackson died on June 25 from a suspected cardiac arrest, and it has been widely alleged he was given surgical anesthetic Propofol by his personal physician Dr. Conrad Murray earlier in the day to help him sleep.
Meanwhile, Michael's family have reportedly requested a third autopsy be carried out on the late pop star's body in order to prove foul play.
His mother Katherine is convinced her son was murdered and wants another opinion on the cause of his death.
A source said: "Katherine looked at the second autopsy and she wasn't happy with what it didn't reveal to her."
The Los Angeles County coroner's office has not yet ruled on the cause of death, with results currently delayed indefinitely.
Police are currently investigating Dr. Conrad Murray on accusations of manslaughter.
