"There are already irregularities," a close family member said.

Maradona's lawyer, Matias Morla, had earlier called for an investigation into claims that ambulances took more than half an hour to reach the football star's house in response to an emergency call on the day of his death.

A preliminary autopsy report established that Maradona died in his sleep at noon on Wednesday (Thursday AEDT) of "acute lung edema and chronic heart failure."

The prosecutor's office in Buenos Aires has opened a file entitled "Maradona, Diego. Determination of the cause of death."

"The case was initiated because he is a person who died at home and no one signed his death certificate. It does not mean there are suspicions or irregularities," a judicial source said, requesting to remain anonymous.

The 60-year-old Argentine football legend was receiving round-the-clock medical care at a house in a gated community in Tigre, north of Buenos Aires, where he was recuperating from surgery to remove a clot on his brain in early November.

"You have to see if they did what they were supposed to do or if they relaxed," the family member said. 

"The nurse made a statement when the prosecutor appeared on the day of Diego's death, then expanded her statement and finally went on television to say that what she said was forced on her, so there is some contradiction in her statement," the close relative said.

The prosecutor's office is awaiting the results of toxicological tests on Maradona's body. 

The three prosecutors working on the case have requested the star's medical records, as well as recordings from neighbourhood security cameras.

Another nurse caring for Maradona was likely the last person to see the star alive, at dawn on Wednesday local time, prosecutors said through a statement on Saturday (AEDT).

"From his words, it could be established that he was the last person to see (Maradona) alive at approximately 6:30 in the morning," as the night shift at the star's house was ending, it said.

The nurse, interviewed by prosecutors on Friday (AEDT), "referred to having found him resting in his bed, assuring that he was sleeping and breathing normally."

Maradona's nephew Johnny Herrera was previously believed to have been the last person to see Maradona, at 11:30pm on Tuesday.

Prosecutors said the nurse present in his house at the time of death told them that she had heard Maradona "moving around inside the room" at 7:30am.

They said that at 12:17pm, "Maradona's personal secretary requested medical assistance, and an ambulance from the company +VIDA was present at 12:28pm, according to film records from the San Andres neighbourhood obtained by the prosecutor's office".

Several ambulances from other medical service providers arrived later.

Investigators have also established that Maradona's personal doctor, Leopoldo Luque, had already made a 911 call at 12:16 pm, requesting an ambulance.