TAIPEI ? Taiwan investigators probing the 2004 shooting of ex-president Chen Shui-bian said Thursday they found no blood or bullet hole in his trousers, adding mystery to an event that may have won him a second term.

Chen, who is now facing life in jail for graft, was slightly injured in the stomach in the apparent assassination attempt less than 24 hours before that year's poll, with critics saying it triggered a crucial sympathy vote.

"Chen was wounded in the abdomen, but why were there no blood stains or bullet hole on his underwear and pants?" said Wu Feng-shan, a member of the team that reopened the probe, according to ETTV news channel.

The investigation was initiated by the Control Yuan, a branch of Taiwan's government in charge of supervising other branches.

After the incident on March 19, 2004, Chen went on to win the vote by a razor-thin 0.22 percent margin, allowing him to serve for a second four-year term.

The Kuomintang party, which fielded the candidate defeated by Chen, accused him of having staged the shooting to garner the voters' support -- a charge he flatly rejected.

Chen's running-mate Annette Lu was also slightly injured during the mysterious shooting, which took place as they were campaigning in an open car in the southern city of Tainan.

Police who ended their probe in August 2005 concluded that a jobless man called Chen Yi-hsiung had shot and wounded the duo.

Ten days after the shooting, Chen Yi-hsiung was found dead in a fishpond near Tainan. Police said he killed himself out of remorse, a finding categorically rejected by the Kuomintang.

The disputed election plunged the island into turmoil for many months, with the opposition leading street rallies demanding Chen Shui-bian's resignation and initiating several failed recall motions in parliament.

The drama took a new twist in 2006 when the alleged gunman's widow -- who previously confessed her husband's role in the shooting -- claimed that she had been coerced by police and demanded a fresh probe.

Chen, who left office in May last year, has been sentenced to life on charges of embezzlement, taking bribes, money laundering, influence peddling and extortion. He is appealing against the allegations.