The accused murderer of a cleaning woman found stuffed into an air shaft in a Rector St. office building two years ago is hoping a forensics foulup will set him free.

Investigators used a single swab to collect DNA from both the outside and under-side of each of the victim’s fingernails, the lawyer for accused murderer Joseph Pabon, the building’s maintenance man, told a jury in closing arguments today.

Pabon’s DNA was recovered from these swabs, leading prosecutors to assert that it got there when victim Eridania Rodriguez scratched Pabon in her struggle for life, allowing the tragic mom to now literally finger her murderer after death.

But “it was one continuous swab taken from top to bottom, which now opens up the possibility that my client’s DNA was on the outside of the nails and got there as a result of the two of them working together,” said defense lawyer Mario Gallucci.

Prosecutor Christine Keenan countered that too much of Pabon’s DNA wound up on the swabs for it to have merely been the few stray cells that might adhere during casual contact. A Manhattan Supreme Court jury is set to begin deliberations tomorrow.