The cause of death on the 50-year-old’s death certificate has been amended to 'homicide' after months of speculation.
According to the document the King of Pop died from ‘acute Propofol intoxication’ due to an ‘intravenous injection from another’.
On the original certificate issued on July 7 deputy coroner Cheryl MacWillie refused to give a cause of death.
However after further investigations, the certificate was amended and re-released in August by medical examiner Christopher Thomas. It now states the cause of death on 25th June 2009 as 'homicide'.
A source said that the Jackson family are 'keeping faith with the police', adding: 'We still feel that there is more than one person responsible for Michael's tragic death.
'Joe won't give up on getting justice for his son and a lawuit is his focus.'
The news comes after it emerged that the singer’s doctor Conrad Murray is expected to be charged with manslaughter.
Dr Murray could be prosecuted for 'gross negligence' for his treatment of the pop star during his last hours, police sources said.
Murray, a cardiologist, was with the star at his rented Los Angeles mansion in June and tried to revive him when he was found unconscious.
Murray already has a Houston law firm building his defence. Police affidavits say he admitted loading up Jackson with Propofol and other drugs in the hours before his death.
Miranda Sevcik, a spokeswoman in Houston for Murray and his lawyer, Edward Chernoff, said Friday the doctor had no comment and reiterated that Murray neither prescribed nor administered anything that should have killed Michael Jackson.
Jackson died while under Murray's care as the singer prepared for an ambitious concert schedule.
The district attorney's office is waiting for Los Angeles police to turn over the case before presenting it to a grand jury, the law enforcement source said.
A spokeswoman for the district attorney's office, however, denied that any decisions have been made.
'We have been working closely with the Los Angeles police during the pendency of this investigation,' spokeswoman Sandi Gibbons said.
'There is no case before us at present and no final decision has been made.'
To prove a charge of involuntary manslaughter, authorities must show there was a reckless action that created a risk of death or great bodily injury.
If a doctor is aware of the risk, there might also be an issue of whether the patient knows that risk and decided to take it.
A large number of witnesses have been interviewed by police, including those who were present during Jackson's last days and those who worked with him in preparation for his comeback concert, 'This Is It'.
Authorities have also lined up medical expert witnesses who will testify about the normal standard of care in a situation such as Jackson's and will give opinions on why Murray's actions constituted gross negligence, the source said.
The police investigation was substantially completed by the end of December, the source said.