In what De Silveira called a "very targeted" break-in, the perpetrators took two Mentor iQ borescopes, an extremely specialised piece of remote visual inspection equipment used by the oil and gas, aviation, defence and power sectors.

Chevron Corporation is understood to have about 20 of them for its Gorgon LNG project, as they are an essential tool when operators need a high level of cleanliness and assurance for a flawless start-up.

The borescope - a 6.1mm high definition camera with a 3m probe on it - enables operators to drill through anything and see what's in it or on the other side, and is a standard tool in airports for engine inspections and for gas turbines, among other things.

It's also the kind of tool seen in Hollywood movies where people break into safes or high-security areas.

The Nexxis property, secured by gates at the front to which everyone in the complex has access, has two offices and a large storage area that is protected by a second set of gates.

The technical equipment company's building has roller shutters that would need to be pried off to allow access, which would then require smashing a window. All the doors are deadlocked, requiring a key to get out.

Nexxis' base is a two-storey building except for a garage which the robbers climbed onto, then drilled into the walls with a self-capping drill so they could grapple up to the second level, climbed onto the roof and cut a hole into it.

De Silveira believes they must have known the internal layout because they missed the offices by just a foot.

"They knew they were close but weren't sure how close and they wanted to get in on the wall side so they could hang off the wall and slide down," he said.

The thieves shifted over a metre and cut another hole into the roof and jumped through it, then went through everything in Nexxis' storage facility.

Seeing everything open from robotic crawlers to laptops, De Silveira got in on Thursday morning thinking his guys must have just had a really busy afternoon and hadn't put it all back.

An employee's purse with credit cards in it and a bottle of single malt scotch sat on a table, with spare car keys in the drawers.

They left it all in favour of some very specific items.

"If they had a truck, there are enough tools in here to get out - though not that there's much you can do with the equipment unless you know how to operate it all," De Silveira said.

"It's all serial numbered and protected, there's no second-hand market for it, and it's all identifiable by us."

Police forensics teams that inspected Nexxis' base in Perth's southern suburbs could not find any finger prints, the only trace being two different sets of boot prints suggesting it was two adults.

Investigators are trying to obtain footage from security cameras up the street, as Nexxis didn't have any cameras installed, something De Silveira now aims to rectify.

A look into what the borescope is used for may provide a clue to who the perpetrators could be, but even there, De Silveira is coming up dry for answers.

"Initially I just thought it was kids having a bit of fun, but the more I looked at it, I realised it was a professional job," De Silveira told Energy News.

"The military uses the borescopes, as do operators to check their plants; the robotic crawlers [also in Nexxis' facility] are used by bomb squads, so it's all very specialised, high-end equipment.

"You can't sell the borescope ¬- Cash Converters wouldn't even know what it is, and a select few would know what it does or what its value is.

"Our competitors would never do it because they know we've got just as much security on our gear as they do, and because we're the only ones who stock this gear so we'd just call GE and they'd tell us whether the competitor just bought one.

"So our competitors are completely ruled out, and besides we actually get along with them quite well. I immediately emailed them and they offered their help and support.

"It's pretty bloody hard to work out who would want it."

Initial investigations have so far led both police and Nexxis' insurance companies to believe it had to be an inside job, but De Silveira - who describes himself as one of the most suspicious-minded people in the world - has already ruled out his own employees as they are like, and in some cases literally are, family.

A former employee?

No way, De Silveira says.

They haven't had any for at least eight months, in which time a lot has changed in terms of stock location and content.

"We absolutely would not have disgruntled employees," he said.

"The last two people that arrived were made redundant by their previous employer. We gave them a chance then they found a job that was more suited to them, so they came back cap in hand thanking us for giving them the opportunity. We said they could come back whenever they like, and we still speak to them regularly."