Rachelle Yeo, 31, a hospital specialist representative, died Monday after suffering from critical injuries believed to be sustained in the middle of an argument. Her former boyfriend is suspected of murder, while her new boyfriend has paid tribute on Facebook, saying she made him happy in the short time they have shared together.

The suspect: Paul Darren Mulvihill

Paul Darren Mulvihill, 44, of Surfers Paradise, was Yeo's former romantic partner. He was a married man when they met, but reports indicate he had left his wife for Yeo.

Mulvihill was the national pharmacy channel development manager at Sanofi Aventis Pharmaceutical. He and Yeo developed an affair while working together in 2007, but their relationship had ended and Yeo moved on.

The victim: Rachelle Yeo

Yeo's LinkedIn profile shows she had worked at Dell computers in Ireland and graduated from the Australian Catholic University.

Yeo had reportedly told a friend about Mulvihill's obsession towards her. When the couple's relationship had become problematic, Yeo turned to friends to talk about what Mulvihill was doing.

"He would send emails, call," one of Yeo's friends told the Herald.

The new boyfriend: Rob Hunt

Rob Hunt and Yeo met in Ireland in 2005 when they both worked at Dell. It is understood their romantic relationship developed only recently.

"I'm very grateful for the short time I got to spend with her and I'm consoled in knowing that she was completely in love with me and in a very happy place in the end," he wrote on Facebook.

Hunt also posted he "adored [Yeo] since we first met in Ireland and since being with her I have been as happy as a person can possibly be."

Witnesses, domestic violence

Neighbours reported hearing a loud argument at Yeo's apartment in Pitt Road, North Curl Curl in Sydney at about 9:20pm Monday night. When officers came in, they had to break down the door. Police found Yeo with critical injuries. Paramedics tried to resuscitate her, but Yeo died a short time later.

Northern Beaches Local Area Commander, acting Superintendent Graeme Pickering, said officers saw a "very unpleasant" crime scene after they broke into Yeo's apartment.

No one has spoken on the specific injuries that Yeo sustained.

"Domestic-related violence will be a line of inquiry. But obviously we'll check everything," acting Superintendent Graeme Pickering said.

Arrest, court hearing

Mulvihill was arrested a day later at Brisbane Airport. He was stepping off a flight from Newcastle when police walked into him. He was charged with Ms Yeo's murder, then extradited to Sydney Wednesday night.

Defence solicitor Tim Meehan told reporters Mulvihill would "vigorously defend himself" in court.

Mulvihill appeared at the Central Local Court Thursday following his arrest and extradition from Queensland. He was denied bail and scheduled to appear back in court on September 13.

Police said investigations on Yeo's murder are ongoing.