It was Monday during the last five minutes of testimony from the last witness for the prosecution that the key piece of evidence came out: DNA found on a 17-year-old rape victim's underwear and on an oral swab taken from a 57-year-old rape victim matched DNA taken from Joshua L. Smith.

Smith, 18, is on trial in Ramsey County District Court on two counts of first-degree criminal sexual conduct. He is accused of raping the teen, who is mentally and physically disabled, in the basement of his St. Paul home on Sept. 8, 2006, and raping and brutally beating the 57-year-old woman shortly after midnight New Year's Day 2007 in the parking lot of the Salvation Army on Payne Avenue.

Smith was 16 at the time of both attacks; he was certified to stand trial as an adult.

Alyssa Bance, a forensic scientist for the state Bureau of Criminal Apprehension (BCA) trained in DNA testing, was assigned on Jan. 10, 2007, to the 57-year-old's case. She found two DNA profiles on an oral swab taken from inside the victim's mouth by an emergency-room nurse before the victim underwent medical tests and later a sexual assault exam.

One of the profiles was from an unidentified male; the other was from the victim. The same two DNA profiles were on a condom found at the rape scene. Bance said the male DNA profile did not match any in the state or national databases. Nor did it match any of the 34 samples that St. Paul police brought to the lab in hopes of finding a suspect.

Under questioning from defense attorney Michael Michalski, Bance said the BCA laboratory maintains a notebook of "unexpected results," when foreign DNA is identified or other mistakes are made. In those cases, she said, testing is redone or determined to be "inconclusive." Bance said the 57-year-old victim's case did not yield any unexpected results.

Jason Simser, another BCA forensic scientist, worked on the case of the 17-year-old and identified a male DNA profile from semen found on two areas of the girl's underwear. One area was a mixture of a male's DNA and the victim's DNA. The other was a "single source" male DNA profile, Simser said.

And the male profile was a 100 percent match to Smith, Simser said. Smith had voluntarily given a DNA sample during a police interview Sept. 28, 2006.

When Smith's DNA sample was uploaded to the databases on Feb. 27, 2007, it also was found to be a perfect match to DNA found in the 57-year-old's case.

Simser explained that a DNA profile matches "not more than one unrelated person in the world's population" or, conservatively, 1 in 100 billion people.

Michalski asked Simser whether he "always testified in favor of the BCA."

"I testify about the conclusions of the testing, whatever they may be," Simser said.

The state rested its case before noon, and Michalski began his after lunch. The first defense witness, Dr. Douglas Olson, is a pathologist and head of the laboratories at Regions Hospital in St. Paul.

He testified that additional oral, facial and genital swabs were taken from the 57-year-old for the hospital's use but no evidence of sperm or seminal fluid was found on them.

Under cross-examination from prosecutor Heidi Westby, Olson said the BCA gets the first swabs taken from a victim and the agency's molecular testing is much more sensitive than the hospital's methods.

District Judge Margaret (Peg) Marrinan told jurors they would likely begin deliberations today after the defense presents its remaining witnesses.

Pat Pheifer • 651-298-1551