A dogged police lieutenant determined to crack the case of slain Queens jogger Karina Vetrano told the court Thursday about a chance sighting, months before the murder, that led him to the accused killer.

NYPD Lt. John Russo, 42, told Queens Supreme Court jurors he first spotted Chanel Lewis prowling around Howard Beach in May 2016.

The next day, Lewis was spotted in the area again and questioned by cops.

Months later, investigators were struggling to solve Vetrano’s murder. She’d gone on a run Aug. 2, 2016, and was found by her father hours later in Spring Creek Park.

Russo remembered spotting Lewis, 22, earlier and instructed detectives to track him down in January 2017.

An investigator went to Lewis’ East New York home to collect DNA and prosecutors say that sample matched DNA found on Vetrano.

Lewis faces life if convicted of murder and sex abuse.