Garda Commissioner Drew Harris has described the suspected murder case of eight-year-old Kyran Durnin as “extraordinary”, saying he has never seen one like it in his 40-year career.
Mr Harris said there is a “particular element” in the disappearance of the schoolboy that is “difficult to comprehend”.
He said that investigators are pursuing the case with “full vigour and resources”.
Gardaí suspect that Kyran may have died in 2022 when he was aged six.
It comes as officers continue to search a former family property and adjoining lands in Dundalk, Co Louth.
Now in its third day, investigators are carrying out a thorough search in and around the property.
A digger was seen working in wasteland directly behind the terraced house as part of the investigation into the suspected murder of the schoolboy.
Last week, gardaí opened a murder investigation months after Kyran was reported missing along with his mother.
The youngster’s mother has been located, but investigators say the whereabouts of Kyran remain unknown and he is now presumed dead.
Speaking to reporters in Dublin, Mr Harris said: “It is an extraordinary incident. I’ve over 40 years now in the police, and I have not seen really the like.
“I cannot think of a similar set of circumstances, and in that way there’s a particular element to this which is difficult to comprehend. But we have our work to do.
“This is a murder investigation and you can be assured that we are pursuing it with full vigour and resources.”
Mr Harris said he was first made aware of Kyran’s case in early September.
“From the very beginning of this investigation, from August 30, it commenced as a missing persons investigation and then very quickly garda members, their suspicions were aroused and I was briefed on this in early September and visited the investigation teams,” he said.
“We have obviously been very concerned to understand what has happened to Kyran and where this investigation is going to take us.
“I don’t want to comment on what our next steps might be in terms of searches and what other investigative steps we want to take.
“But you can be assured it is fully resourced and it continues at pace.
“We have received a lot of information from the public, certainly since last week, with important information.
“We encourage anyone who might know anything to come forward.
“What we have worked at is to try and identify proof of life since the last actual sighting in 2022, so I cannot comment specifically on whether Kyran reached his seventh or eighth birthday.”
Minister for Justice Helen McEntee said the country is devastated over a young boy possibly missing for two years, and not known to anyone, including authorities.
“The death of any child is devastating, particularly where children are vulnerable and where a child is engaged with state agencies or is in our state services, and they are particularly vulnerable. There is an onus to do everything we can to protect them,” the Fine Gael minister said.
“If there was a failure, we have to understand what has occurred here and how we make sure it doesn’t happen again.
“If people need to be held accountable, that happens too.
“The objective here is to find him, we don’t know where he is and the gardai are working hard to do that, to understand what has happened, and if people need to be held accountable, that it happens, because no time, expense, nothing is being spared here.
“Every effort is being made to make sure we can identify where he is and lessons need to be learned here, and changes need to happen.”
It emerged that the Child and Family Agency, Tusla, said it raised a “significant concern” around the missing child to police in August.
