By Debabani Majumdar
BBC News, London
Nine years after Surjit Athwal disappeared, her mother-in-law Bachan Athwal and husband Sukhdave Athwal have been jailed for life for her murder.
Surjit began an affair with a work colleague
The Crown Prosecution Service (CPS) said its biggest challenge was proving she was murdered without a body.
Securing evidence was very difficult and grew harder as the investigation was spread over four countries, Devi Kharran, senior crown prosecutor, said.
She said the case sent a strong message that there was "no honour in murder".
Ms Kharran said: "It's been very difficult from the start to finish. The most difficult was to prove a murder without a body - the body was never found."
Surjit, who was 27, accompanied Bachan to a family wedding in the Punjab, India, in December 1998, but she never returned.
It subsequently emerged that Surjit, who wanted a divorce and to start a new life with her lover, was killed to save the "family honour".
Surjit, a customs officer at Heathrow airport, was married to Sukhdave Athwal at the age of 16 and had two children with him.
As her marriage with Sukhdave was falling apart she fell in love with a work colleague.
Before her visit to India, she told the family that the marriage was over and initiated divorce proceedings.
Bachan Athwal said she wanted to defend the family honour
Ms Kharran said prior to the trip Bachan held a family meeting in her west London home where it was decided to "get rid" of Surjit.
The court heard that at the wedding, a relative and another person strangled and then dumped her body into the River Ravi.
The CPS said it was aware that in India a person was tried and acquitted of kidnap.
On returning from the trip the pair told Surjit's family and children she refused to return home.
The family then removed her name from the deeds to the family home in Hayes, north-west London, and got rid of all photos of her.
'Frightened to speak'
Ms Kharran said in so-called honour killing cases families were often tied up in the situation.
"Family members are frightened or unwilling to speak and don't want to jeopardise their position in the family structure."
Sukhdave and Bachan were arrested in 2000 on suspicion of conspiracy to murder but were later bailed.
But in 2005 a daughter-in-law was coaxed into speaking by her father.
Then Bachan's daughter, who was later declared a hostile witness, told the police about the family meeting where they decided to "get rid" of Surjit, Ms Kharran said.
Surjit's boyfriend also testified in court.
"The daughter gave evidence from behind a screen as she was very frightened and apprehensive as she was giving evidence against her own mother."
Those statements saw Bachan and Sukhdave charged with murder in 2005.
Evidence gathering was challenging for police who had to visit India, Norway, Singapore and Canada.
Sukhdave married Surjit when she was 16
Police spoke to Sukhdave's two ex-wives, in Norway and in Singapore.
Officers also visited Canada to see if Surjit had started a new life with her boyfriend there.
But it was India that caused investigators problems, Ms Kharran said.
"We submitted a letter of request (for officers to visit) in early 2006.
"It took nine to 10 months for India to allow our police to investigate... the 10-month delay jeopardised the initial date when the trial was scheduled begin."
As the "jigsaw pieces" started to fall into place, a well-thought out plan emerged.
Ms Kharran said: "We find no honour in a murder and the most important thing for us is to have sufficient evidence to provide a realistic prospect of conviction and if satisfied we would prosecute anyone who commits these crimes in the name of honour."
"This will send out the right message to the community... If you commit a crime in another jurisdiction or country and return, and if you are a British citizen the CPS can still prosecute you."