The prosecution will be allowed to introduce fresh evidence in a criminal appeal only if it meets strict conditions, even if these might be relaxed for the accused.

This was made clear by the Court of Appeal when it rejected a prosecution witness' testimony submitted as part of the State's attempt to overturn a not-guilty verdict for a 57-year-old man accused of raping his lover's teenage daughter.

The apex court - comprising Chief Justice Sundaresh Menon and Judges of Appeal Andrew Phang and Judith Prakash - held in judgment grounds yesterday that the "new" evidence could have been presented during the trial.

They also justified why courts are "more accommodating" towards fresh evidence put forward by the accused, highlighting the need to prevent wrongful convictions and the disparity in resources between the State and the defence.

"The law strains against and works doubly hard to prevent any erroneous deprivation of liberty," said the court.

In April last year, the accused was cleared of all sexual offences against his lover's daughter, who claimed that he drove her to a forested area in Punggol in a prime mover and raped her when she was between 15 and 16 years old. The man said he had never driven the vehicle, and his employer testified that the prime mover was driven by someone named Idris, who died before the trial.

The trial judge also found that there were no reasons for the girl's failure to promptly tell her family and boyfriend about the alleged assaults, and when she eventually broke her silence, her accounts were "contradictory and inconsistent".

The alleged offences were said to have taken place between 2009 and 2011 but came to light only towards the end of 2012.

The prosecution appealed, and also applied to introduce two sets of evidence - a sworn statement from Idris' son to rebut the employer's testimony, and an expert report from a senior government psychologist to address the trial judge's "misconception of what is typical rape victim behaviour".

Defence counsel Abraham Vergis of Providence Law Asia resisted the prosecution's bid.

Yesterday, the apex court rejected the rebuttal evidence but allowed the psychologist's report for the appeal, which will be heard at a later date.

Ordinarily, an appeal court will not consider new evidence unless three conditions are met: it was not available during the trial; it is relevant; and it is reliable. These criteria were laid down in the seminal English Court of Appeal case of Ladd v Marshall in 1954, which has been adopted by courts here - although a more liberal approach has been favoured in cases where the accused is appealing against conviction. In the current case, the question was whether the prosecution should be given the same leniency.

The court concluded that while a "more accommodating attitude" towards applications by accused people is justified, the conditions set out in Ladd v Marshall should continue to apply "in an unattenuated manner" to applications by the prosecution.

The court said that there is a need to avoid the prejudice that an accused person would suffer if he is wrongfully convicted or receives a disproportionate sentence. There is also a disparity of resources - the prosecution works with law enforcement agencies, including the police, which have wide-ranging powers to collect evidence, the court noted.

Finally, the court recognised that the "harrowing" experience of defending criminal charges is likely to have an effect on the accused's ability to "fully and soundly consider the nature of the evidence he will need at trial".

In the current case, the court found that the evidence of Idris' son failed to meet the condition of non-availability. The court noted that the prosecution became aware of Idris' existence during the trial, but chose not to seek an adjournment for further investigations.

As for the psychologist's report, the court found that it satisfied all three conditions.