A British woman on death row in Texas made a final bid this week to avoid execution and have her case re-tried. Her family and campaigners claim that she was not properly represented at her original trial and that she is innocent of the murder for which she was convicted.

Linda Carty, 50, a former primary schoolteacher, was sentenced to death in 2002 after being convicted of taking part in the murder of 25-year-old Joana Rodriguez. Her legal team this week filed grounds for an appeal in a bid to overturn her conviction and death sentence in the state with the highest rate of executions in the US.

Carty was born in St Kitts and has British citizenship as a result of the Caribbean island's status at that time. She worked as a teacher there before moving with her family to Houston, Texas, when she was 23.

In Houston, she was approached by the police because the man she was dating at that time was, unknown to her, a drug dealer. She became a confidential informant (CI), passing on information about dealers and occasionally making test purchases of drugs on behalf of the Drugs Enforcement Administration (DEA). As a result of this work, she claims, she inevitably made a number of enemies.

In 2001, three men broke into the apartment where the murder victim, Rodriguez, lived with her partner, Raymundo Cabrera. The men demanded drugs and stole a small quantity of cash. They also beat and bound Cabrera and his cousin, Rigoberto Cardernas, and abducted Rodriguez and her four-day-old son, Ray. The baby was later found unharmed in a car, but Rodriguez was suffocated to death after being bound, her mouth duct-taped, and a plastic bag placed over her head.

The prosecution's case was that Carty was afraid of losing her common-law husband, Jose Corona, and thought that, if she had another baby, he would stay with her. It was alleged that, because she was unable to conceive, she hired the men to kidnap a pregnant Rodriguez and remove the baby, using a pair of "surgical scissors".

Initially, Carty was represented by a local lawyer, Jerry Guerinot, some of whose other previous clients are also now on death row. According to the organisation Reprieve, which has taken up Carty's case, and her current lawyers, no proper defence was mounted and she was not aware of her rights to consular access as a British citizen.

Many of the discrepancies in the case against her were not challenged in her trial. Most glaringly, Rodriguez had already given birth so Carty, who lived in the same apartment complex as her, could hardly be accused of trying to remove the baby from the womb.

Vitally, two key witnesses, her common-law husband and her DEA contact, both of whom could have helped her case, were never contacted by the defence team. Her DEA contact, Charlie Mathis, might have been able to testify to the extent of Linda's DEA work but was not asked to do so by the defence. In October 2005, Mathis swore in an affidavit that he could have given evidence that would have significantly aided her defence. "I found it odd that Linda's attorneys never even attempted to contact me, let alone talk with me about my testimony at Linda's trial," he said.

In his affidavit, Mathis stated: "I would have been willing to testify that Linda should not have gotten the death penalty and also would have been willing to testify that I do not believe her to be a future danger. I would have testified that she is not a violent person, let alone a cold-blooded murderer."

"When I began this case, I was pro-death penalty," said Mike Goldberg of the law firm, Baker Botts, which is now representing Carty. "But the facts are so outrageous that my firm is sparing no expense to get Linda Carty a new trial."

Goldberg claims that key witnesses were never contacted.

Clive Stafford Smith of Reprieve said: "It is time for the British to get seriously worried about Linda. She has not come close to a fair hearing so far - her lawyer presented virtually no defence, and no court has since taken her case seriously."