He said many of the management were ex-prison officers from Scotland who had introduced new measures including daily lockdowns at the centre, home to both non-Australian citizens facing deportation because of criminal convictions, and asylum-seekers. He said the centre's residents were kept segregated into six zones with one zone for women and another a "management unit" where detainees were kept in isolation for "any perceived breach of centre regulations". "[The] lockdown experiment started a year ago and since then [violent] incidents have escalated," he said. "The centre is in lockdown after 8pm, [so there is] no free movement or access between zones after 8.30 at night." The source said out of 24 hours, the residents were only allowed "two hours maximum" to access meals and gym outside their zones.

"Earlier there was an aspect of welfare; at the moment it is correction," he said. Australian Border Force took over the management of the centre in July 2015, at the same time as the Department of Immigration and Border Protection merged with the Australian Customs and Border Protection Service. The day-to-day running of Maribyrnong falls to Serco, a private security firm that has contracts at a number of detention centres. A Department of Immigration and Border Protection spokesman said Border Force had a "more active role" in all levels of management, with the government agency directing "day-to-day operations" and "working directly with service providers" to ensure the facility was "safe and secure". The Department's spokesman said the detention centre's population was changing with more "high risk detainees" prompting the government to "implement a range of controls to mitigate any violent or criminal behaviour".

He said this included the separation of detainees and "certain cohorts" and "controlled movements" within the centre. "The Department is committed to the good order of the detention network, and will continue to work with Serco to ensure that Australia's immigration detention facilities are as safe and secure as we can make them," he said. "This includes ensuring that appropriately trained Serco officers have access to safety and security equipment, including personal protective equipment." As Fairfax Media revealed in January, Maribyrnong detention centre has a higher incidence of use of restrains and handcuffs than at any other detention facility under the control of the federal government. The source said the staff were increasingly being forced to act like prison officers, despite being hired as client service officers.

"There are a lot of people who have got a lot of issues with the kind of work they have to do," he said. "Staff are always on edge." He said close to one-third of the staff had been on stress leave in the past year, with some returning to administrative and light duties work since. Broken security infrastructure and caring for mentally ill patients also increased the pressure on staff, he said. Confidential documents seen by Fairfax Media reveal that over a three-week period in July 2015, many of the centre's cameras and alarms were faulty, despite repeated complaints to Serco management.

In one instance, as many as 82 of the 135 cameras were not working over a 24-hour period, with 67 cameras not recording, and 15 not connected in the day. During the night, 71 cameras were not recording and 13 were not connected. One of the entries by an officer states that it was discovered the camera was not recording "after an attempted escape". The logs also show that on three separate occasions, two detainees who were on a "high imminent" suicide watch were kept in a room with no cameras to monitor them. The source said there was also a lack of adequate care for mentally ill detainees at the centre. "If somebody is on a suicide watch …they have people observing them … but there is no medical staff looking after them."

The Department's spokesman would not say how many of the staff had been on stress leave in the past three years; however, he said, staff had access to free counselling services. The spokesman said the Department took very seriously "its duty of care" towards the detainees and provided them with medical and mental health services "equal to, or above" those available to Australians. This included "constant person-to-person supervision" for those at risk of self-harm. He said all cameras and alarms were checked daily and maintained monthly, quarterly and annually, with set timeframes for contractors to carry out any repairs. He said all the cameras and alarms were working as at February 23. United Voice Victorian Secretary Jess Walsh said stress levels at Maribyrnong amongst detention officers were rising. Ms Walsh urged national Serco management to step in and provide support.

Refugee advocate Pamela Curr​ said security at the Maribyrnong centre was getting "tighter and tighter" incrementally since the ABF took over. "The Border Force arrive on duty in the morning and people tell me that they stride around both MITA [Melbourne Immigration Transit Accommodation] and MIDC [Maribyrnong] as a show of force – every day in their uniforms," Ms Curr said. "The staff are all scared, absolutely petrified. They are constantly looking over their shoulder [for fear] of being caught out, breaking some rule. "The guys who have been there a long time say 'I use to live in a detention centre [but] now I live in a military camp'."