The Mexican official in charge of the investigation into the brutal slayings of an Ontario couple says the principal evidence linking the two Canadian women to the murders is a trail of blood.

"A trail of blood led from the crime scene to the suspects' room," said Bello Melchor Rodriguez y Carrillo, attorney general for the state of Quintana Roo, where the murders of Domenico and Annunziata Ianiero took place.

"There are traces of blood on the key slot, the remote control, the refrigerator, the bathroom taps," he told CTV's Denelle Balfour in Spanish.

The attorney general conceded it's not yet clear who the bloody fingerprints belong to, and tests have yet to reveal if it's the same blood from the crime scene.

Still, he disagreed with witness reports that the blood was either tracked or cleaned up by hotel staff.

Authorities originally characterized the killings as the work of a professional -- fuelling speculation about a possible link to organized crime.

While Rodriguez later recanted that theory, he backtracked his statements in his interview with CTV News and repeated the initial allegations.

"The evidence is clear. The Canadian couple was killed by professionals with experience in these kinds of jobs. It was not done by an amateur," he said.

Rodriguez alleged the killers tried to clean the blood in the hall and in their room, but that traces were later revealed in forensic tests.

While he has stuck to his claims that two Thunder Bay women, Cheryl Everall and Kimberly Kim are suspects, he is not currently seeking their extradition.

"Not at this moment," he said. "They are only suspects. We don't know for sure if they committed the crime."

The investigation has faced intense scrutiny from critics who fear authorities botched the probe in their hasty efforts to protect the country's lucrative tourism industry.

But despite reports to the contrary, Rodriguez rejected witness accounts claiming the crime scene had been compromised and insisted the building was sealed, and that staff and guests were questioned.

"We don't have anything to hide. The crime scene is secure. We invite any of the authorities in Canada to review our work," he said.

While Mexican authorities believe the blood has been spread by the suspects, a senior Canadian official close to the investigation has told CTV News the blood was not spread by the women, but by a hotel maid.

The source said the maid likely transferred blood on a cleaning rag from the hallway to Everall and Kim's recently vacated room, information that was bolstered by a Canadian tourist who just returned from the resort.

"They cleaned the room, then they re-rented the room. And then they decided to look at that room ... after they'd rented it, and moved the people from that room, like at midnight. They woke them up, got them out of bed, and decided to search the room then," Brady Scavarelli told CTV.

RCMP stands by controversial probe

Despite allegations that the investigation has been botched, the RCMP's top brass is standing by the controversial probe.

"We have full confidence in the Mexican police and in their ability to carry out this investigation in the proper fashion. To date, there has been full co-operation," Assistant Commissioner of Federal and International Operations Raf Souccar said at a news conference on Thursday afternoon.

Souccar told reporters the RCMP liaison officer stationed in Mexico was informed of the deaths of Domenico and Annunziata Ianiero as soon as their bodies were informed. In turn, the liaison officer contacted the Mounties in Canada.

"We, in partnership with Interpol Ottawa and other law enforcement agencies have been in contact with the Mexican authorities, and we have offered them our full support," Souccar said.

He sought to assure the Ianiero family and all Canadians that the RCMP will continue to do everything in their power to see that the investigation was brought to a professional conclusion.

But he emphasized that the murders took place outside the jurisdiction of the Mounties.

"It's important to remember that this is a Mexican investigation, as with almost any investigation into crimes outside of Canada, international law limits the extent to which we can participate," he said.

Souccar downplayed suggestions that the crime scene has been tampered with, and that the investigation has been botched.

"They've collected whatever evidence needs to be collected. As I said, I've got full confidence in their ability to uncover what needs to be uncovered and to ask for what needs to be asked for," he said.

Meanwhile, police in Thunder Bay, Ont. say they've interviewed about 20 local residents who were at the same Mexican resort as the Ianieros.

The investigation in the northwestern Ontario city was launched after local authorities received a request from Mexican police through Interpol earlier this week.

"We're still working with a list of approximately 50 and we have just shy of 20 that we've interviewed so far," police spokesman Chris Adams told The Canadian Press.

Neither Souccar nor Adams would comment on the status of Everall and Kim.

"At this point we don't exclude anybody, we don't include anybody," Souccar said, noting that the RCMP had not received any extradition requests.

"All individuals we have reason to speak to, we will speak to."

Foreign Affairs Minister Peter MacKay is scheduled to meet Friday in Ottawa with his Mexican counterpart Luis Ernesto Derbez Bautista.

With a report from CTV's Denelle Balfour and Jill Macyshon