Portuguese police have offered the mother of a missing four-year-old British girl a plea deal if she admits she had something to do with her disappearance four months ago, according to a family member.

Madeleine McCann's aunt, Philomena McCann, told British news agencies on Friday that police made an offer to the missing girl's mother, Kate McCann.

Kate McCann, the mother of the missing girl, arrives at the police station in Portimao, Portugal, to be questioned Friday.
(Miguel Angel Morenatti/Associated Press)

Philomena McCann told Britain's ITN that Portuguese police "tried to get Kate to confess to having accidentally killed Madeleine by offering her a deal through her lawyer."

"Part of it is they're trying to get Kate to admit to having accidentally killed Madeleine and disposed of her body,"  Philomena McCann told the news agency.

Family members also say police have named Kate McCann as a formal suspect, or "arguida," in the case.

Police in Portugal have only confirmed they have a new suspect in the case, but have not identified anyone. Kate McCann was questioned by police on Friday in Portimao and later released.

Gerry McCann, the girl's father, also arrived at the police station for separate questioning on Friday.

A handful of people in the crowd booed as Kate McCann arrived at the police station in Portimao, a town in Portugal's southern Algarve region, on Friday morning for her second police interview in as many days. She was questioned for almost 11 hours Thursday.

A family spokesperson said she has been formally declared a suspect and the father, Gerry, expects the same. Police would not confirm the reports.

The father arrived at the police station shortly before 11 a.m. ET Friday, just as Kate exited the building.

Bloodstains in couple's rental car

Under Portuguese law, an "arguido " or formal suspect is someone treated as more than a witness, but has not been arrested and charged. As such, the person has the rights to legal representation and to remain silent during questioning.

The latest development is apparently the result of bloodstains found in the couple's rental car.

Family spokeswoman Justine McGuinness told CBC that police believe blood found in the car rented 25 days after the girl's disappearance suggests the parents were involved in their daughter's death.

"It's been suggested [Kate] is in some way connected to the death of her daughter, which is clearly ridiculous. She's done everything in her power to find her gorgeous daughter Madeleine," McGuinness said.

What does "arguido" mean?

Under Portuguese law, the term arguido refers to officially named suspects. As a suspect, the person has more rights than a witness, such as the right to remain silent and the right to a lawyer. People questioned in a criminal investigation can request arguido status so as to secure those protections not offered to witnesses. If someone is named an arguido, it does not mean they have been arrested or charged, but it can be a first step in the process. A judge can place restrictions on the suspect, such as instructing the person to stay in the country and to regularly report to police. They can also ask that the person be kept behind bars.

Madeleine McCann disappeared May 3 from a vacation apartment in Praia da Luz, a town on Portugal's southern Algarve resort coast, while her parents say she was sleeping in the apartment with her two-year-old twin siblings.

'We will fight this all the way': father

Her parents, both doctors from central England, said they were eating dinner in a restaurant 50 metres away, but checked on the children regularly during the evening. The couple has repeatedly denied involvement in their daughter's disappearance.

Since Madeleine went missing, the McCanns have remained in Portugal, running a website about the search for their missing daughter and trying to keep the media spotlight on the case.

In his blog entry Friday on the website, Gerry McCann rejected suggestions of Kate's involvement in the case as "ludicrous."

"We will fight this all the way and we will not stop looking for Madeleine."

Madeleine McCann, shown above in an undated family photo, went missing during a family holiday in Portugal.
(Associated Press)

The two had been planning to leave Portugal on Sunday, but Portuguese police urged them to remain in the country, suggesting an imminent breakthrough in the case in connection to DNA evidence.

Both have been interviewed by police in the past. On Thursday, it became public that the mother would be formally re-interviewed Thursday, followed by the same for the father on Friday.

Detectives had stressed Thursday that they were interviewing the parents as witnesses, not as suspects.

With files from the Associated Press