An ex-soldier from Leicester and his brother, a "callous and calculating" cash-and-carry worker from Coventry, have been found guilty of murdering a marketing manager who was smothered with chloroform on Christmas Eve.
Costco store boss Roger Cooper, of Tilehurst Driver, Coventry, and ex-soldier David Cooper, of Hughenden Road, Leicester, bought poisonous metals, identified a shallow grave and communicated in text messages written in a Star Wars-based code before killing Sameena Imam, from Cardiff.
An eight-week trial heard that Roger Cooper spent at least a month plotting to kill the 34-year-old - one of his three lovers - to prevent her exposing theirtwo-year affair.
Both Roger and David Cooper - who are 6ft 5ins and 6ft 7ins tall - remainedcalm and did not look at each other as they were unanimously convicted by a jury at Birmingham Crown Court.
Miss Imam, who was just 5ft 2ins, is believed to have been overpowered on a sofa at David Cooper's home in Leicester, between 5.07pm and 6.26pm on Christmas Eve, after being driven to the property from Coventry by hisbrother.
The victim, who worked at Costco stores in Cardiff, Southampton, Bristol and Coventry, was reported missing by family members in Essex after failing to return home for Christmas, sparking a major police inquiry.
Roger Cooper, 41, and his 39-year-old brother were arrested on suspicion of murder on January 7 - a week before Ms Imam's body was found buried on an allotment in Leicester.
Post-mortem tests established that the shop worker, who lived in Cardiff, was killed using chloroform.
A "bizarre" combination of metallic elements, including antimony, cadmium,tin, mercury and arsenic, is also thought to have been administered to Ms Imam in a liquid.
At the start of the trial, it was alleged that Roger Cooper was "juggling"relationships with three women, including Sameena and a second colleague, while managing Coventry's Costco warehouse.
The retail worker, of Tilehurst Drive, Coventry, told police investigating MissImam's disappearance that he last saw her when she left the store at about 4pm on December 24.
His brother told officers he did not even know Miss Imam's name but later made a partial confession, claiming to have pressed a chloroform-soaked tea towel over her mouth.
Although the former signals regiment reservist claimed the death had been an accident, he later changed his account, telling jurors he found Ms Imam's body after being asked to move a car.
But messages sent from a mobile phone linked to David Cooper - including Stars Wars-related phrases such as "Death Star complete", "stay on target" and "look at the size of that thing" - proved the brothers had made a previous attempt on Ms Imam's life in mid-December.
Roger Cooper admitted in court that a message reading "You are expectedVader" was a coded reference to Miss Imam but insisted it had been part ofsurveillance to check if she was seeing another man.
Other evidence used to convict the brothers, originally from Essex, includednumerous automatic number plate recognition "hits" showing vehicles they had used travelling between Coventry and Leicester.
A bottle of Bellini bought in Coventry by Miss Imam on Christmas Eve was also found in the fridge at the home of David Cooper, whose allotment shed featured a sign reading: "Don't wind me up... I'm running out of places to hide the bodies."
Officers believe the plot on December 11 may have been aborted because Miss Imam arrived at a hotel in Solihull in a taxi and was dropped off within yards of the main entrance.
Evidence of a further suspected attempt to target the regional marketingmanager on December 21 was also presented to the jury.
Detective Chief Inspector Caroline Marsh said:
I would say this is the most callous offence I have ever investigated.