Bottler's enemies planted a tracking device on his car
The intended target of the gruesome double murder had recently discovered a tracking device on a car he used.
Ballymun criminal Derek 'Bottler' Devoy (37) has been involved in a bitter local feud for more than a year and is considered the chief motive for Wednesday's gangland attack.
Last night it emerged that gardai were made aware that Devoy had found the device, which his enemies were using to track his movements.
The discovery was made earlier this month and it is understood that the device was handed over to detectives at Ballymun Garda Station.
Senior sources said gardai were braced for revenge attacks following the shooting.
Volatile criminal Devoy is said to be "completely devastated" about the shocking murder of his sister Antoinette (48) who was killed along with his friend Clinton Shannon (30) in a hail of gunfire.
Gardai are investigating reports that Bottler was spotted storming topless around streets near his home in the early hours of yesterday morning "screaming and roaring".
"Obviously, this is a very, very serious situation," one source said.
"Devoy has been advised to leave Dublin for a few days but he is not an individual who normally listens to garda advice.
"Ballymun is going to be on lockdown now.
"The word is that Bottler was going around like an absolute nutter. He loved his sister, he is completely devastated.
"Everyone is worried about what happens next."
Sources also confirmed that Devoy was recently officially warned by officers about an active threat on his life as part of the Ballymun feud.
There had previously been fears that Devoy would avenge the murder of his brother Michael 'Mad Mickey' (41).
Ultimately this did not happen. A significant reason for this, gardai believe, was that Mad Mickey was murdered by members of the Kinahan cartel, an organisation that Devoy would not have the firepower to tackle.
Devoy was released from prison in February 2015, where he was locked up since 2007, after serving separate sentences for the attempted armed robbery of a post office in Balbriggan and a non-fatal drive-by shooting at two of his neighbours in Ballymun, in 2005.
At the drive-by shooting trial in 2007, evidence was given of how he was recognised when a scarf slipped from his face after he shot at the two men from a car which then drove away at speed.
Just months after being released from jail, Devoy fled Ireland and the Herald revealed that he was in the process of moving more than €100,000 to a bank in the UK when his account was frozen by detectives in Dublin.
The 'going-away money' was frozen under the Money Laundering and Terrorist Finances Act 2010. Devoy returned to Ireland more than a year ago and has been regularly spotted in the company of other criminals.