When you go to the trial of the man who sank a knife into your friend Stephen's heart as he walked home talking to his mother on his cell phone, you think you've already heard the worst. But during the next eight days of evidence and testimony, you realize you were wrong:

As you hear the killer's girlfriend say she punched Stephen in the mouth after he fell, and later they "felt bad" as they washed Stephen's blood off their hands, but then "got down to business," and figured out how to use his credit card to buy cocaine.

As you see the defense display Stephen's khaki shorts, drenched in blood, to argue that the pockets were still clean enough to warrant DNA analysis.

As you hear the man who held Stephen as he died testify that his final word was "mom."

As you see Stephen's 80-year-old grandfather bow his head at crime scene photos of the pool of blood on St. Paul Street that night, as a detective testifies there was so much that it ran into a nearby storm drain.

You walk stunned out of the courthouse each day, onto the streets, where life continues, and where 14 more people have been murdered in the last 30 days, including two 15-year-old friends (one white, one black) shot to death in West Hills.

Stephen Pitcairn loved this city. Hundreds of people attended his memorial services, even though he never got to celebrate his 24th birthday. And despite the sordid and heartbreaking details of his murder, Stephen's spirit touched that Baltimore courtroom too.

On the trial's sixth day, the defense's DNA expert brought up something called Locard's theory of evidence transfer, which underpins the science of forensics, and states, quite simply, that every contact leaves a trace.

In that moment, unknowingly, he precisely conjured up the essence of Stephen Bradley Pitcairn.

Stephen touched people. He made friends in labs and classrooms and buses and streets around this city and the rest of the world. No one ever forgot him.

Stephen's every contact left a trace.

Jacqueline Asplundh, Baltimore