The fence-jumper who wandered around the White House complex for 17 minutes was able to elude the Secret Service in part because the agency has taken down alarm sensors along an area of one fence that he scaled, according to two sources familiar with details of the incident.

The intruder, identified as Jonathan Tran, was able to jump over three different fences, including at least one between the Treasury Department and the east area of the White House complex shortly before midnight March 10.

Tran was able to scale that particular area of the fence without setting off alarms because they had been removed, leading to confusion among officers about his whereabouts and whether an intruder was inside the White House complex, the sources told the Examiner.

The initial fence Tran jumped did trip alarms in that area of the fence-line, but squirrels or even birds sometimes also set off the sensitive sensors, which could have lead to uncertainty about whether someone had jumped the fence or not.

Secret Service personnel removed the alarm sensors along an area of fence line when the agency raised its height in response to previous fence-jumping incidents as a way to make it harder to scale, the sources told the Examiner. Ironically, the very effort to prevent fence jumping appears to have permitted a particularly egregious intrusion.

One source said superiors in the Uniformed Division told Secret Service personnel to remove the sensors and piece them together for use elsewhere. They were never replaced.

Sensors might need to be replaced because they are overly sensitive and always going off or if they are malfunctioning, a knowledgeable source said. Another said that area was particularly prone to false alarms because of birds landing on the fence-line and tripping the sensors.

There are at least 10 to 12 officers and agents, including supervisors from the Presidential Protective Division, monitoring these sensors at any given time. They do so from the Joint Operations Command Center or JOCC, which is located outside of the White House complex.

Some agents and officers also are questioning why Secret Service never released the K-9 unit to try to find an intruder after the alarms on the first fence the intruder scaled went off.

A dog from the K-9 unit was only called in after the man was detained, in order to inspect the backpack for explosives.

Secret Service officers involved were alarmed when the dog sat by the backpack — a signal that it had detected explosive materials, one source said.

A Secret Service Explosive Ordnance Disposal, or EOD, team, located in an office outside the White House complex, was then brought in to screen and clear the backpack, most likely using a robot to do so. After 3 hours of work, the team determined that it did not contain explosive material, the source said.

Most of the dogs the Secret Service uses are Belgian Malinois, a breed trained to detect and stop intruders of any kind. The agency is concerned about releasing the dogs too soon and possibly harming people and other animals but they are mostly muzzled so would not do lasting damage if let loose on the South lawn in order to find an intruder, the sources said.

Early during President Obama's first term, the top agents charged with protecting the president and his family on the Presidential Protective Division were concerned about Secret Service dogs attacking Bo, Obama's first Portuguese Water dog and beloved pet, a source said.

Joseph Clancy, who would go on to lead the agency for two years before retiring in early March, initially shared the concern about the dogs possibly attacking Bo.

But after a fence-jumper made it inside the front door to the White House and into the heart of the first floor in 2014 without the dogs being released, Clancy changed his mind about using the dogs and encouraged it, the source said.

Clancy, a trusted part of Obama's protective detail early in the president's tenure, left the agency in 2011 for the first time to head security for Comcast. He returned in 2015 when Obama tapped him to become the director and left in early March after two years.

Rep. Jason Chaffetz, R-Utah, who chairs the Oversight and Government Reform Committee, is leading an investigation into the March 10 fence-jumping incident, which he said Monday shows that "big changes" are still needed at the Secret Service. Chaffetz planned to meet with Secret Service Acting Director William Callahan and Department of Homeland Security Secretary John Kelly early Monday night.

On March 10, Tran was caught only when he strolled up to the back door and told the Uniformed Division officer posted there that he had an appointment with President Trump, the Examiner reported last week.

In previous reports, the Secret Service was not forthcoming about Tran's ability to elude them and did not disclose that he reached the back door.

At one point while walking along the exterior wall of the East Wing of the White House, the intruder, who was wearing a backpack and carrying two cans of mace, peered inside a window, according to two sources and a court affidavit from the Uniformed Division officer who arrested him.

An Emergency Response Team Secret Service officer detected a man in khaki pants who didn't seem like he belonged there and reported it over the radio system but simply described him as an unidentified man, but not as an intruder, one source said.