Officials investigating the disappearance of 43 students in Mexico have confirmed they were kidnapped, murdered and incinerated by police.

Families of the victims believe their loved ones are still alive – but for the first time, Mexico's attorney general has said he is certain that all of the students were killed and burned before their remains were thrown into a river.

Jesus Murillo Karam also rejected claims that the army had any participation in the mass slaying.

He added: "To close the investigation is perhaps not the appropriate word, until I have all of those responsible under arrest I can't close it, so that is not the right word.

"But if you ask me if the elements of the investigation are enough to conclude that they were killed there and incinerated, I would say 'yes', and even more than in many other cases."

The case has caused considerable controversy in Mexico, with some fire experts claiming the government's rendition of events is implausible.

However, forensic evidence suggests that the fuel and temperature of the fire at the garbage dump was capable of turning 43 bodies into ashes.

Mexican authorities have only been able to identify the DNA of one student, and Austrian scientists working on the case have claimed it is impossible to identify the other victims.

Relatives of the missing students have said they no longer believe a word the government says, as the theory of what happened to their loved ones has continually changed since they were last seen in September.

The brother-in-law of one victim, Valentin Cornelio Gonzalez, said: "On a personal level, it makes me mad because this is what they've always done.

"There's no chance that the parents are going to believe the government saying they're dead… they are going to look for them alive."

The conclusion that all 43 students have been killed is based on the testimony of a prime suspect arrested a fortnight ago.

Felipe Rodriguez Salgado is one of 99 people who have been detained in connection with the crime.

(Sky News)