Two men were arraigned in Suffolk County courtrooms today for unrelated Boston homicides that occurred more than 20 years apart, District Attorney Daniel F. Conley said.

“Some cases are built in a period of days and some over decades,” Conley said. “But no matter when they occur, each one has the full attention of committed detectives and driven prosecutors who refuse to let go when there’s a chance of finding justice.”

KARL PRESCOTT (D.O.B. 1/18/83) of Everett was arraigned in Roxbury District Court this morning on a murder charge stemming from the shooting death last year of 27-year-old Paul Fagan. A few hours later, EUGENE SUTTON (D.O.B. 5/16/65) of Dorchester was arraigned in Suffolk Superior Court for the fatal stabbing of Richard Gleason, 38, in 1989. Both men were held without bail, Conley said.

At Prescott’s arraignment, Assistant District Attorney Jennifer Hickman told the court that Fagan was shot in the back and chest in the area of Dennis and Stafford streets in Roxbury just before 8:00 p.m. on May 2, 2010. He later died of those injuries at Boston Medical Center.

Prescott’s name came to authorities’ attention early on in the investigation, Hickman said. In the weeks and months that followed, she told the court, Boston Police homicide detectives and Suffolk homicide prosecutors made extensive use of cell phone records and cell tower maps, which showed him to be “within yards of where Paul Fagan was murdered” on that night, Hickman said. Those records also refuted Prescott’s statement that he was in Everett on the night of the incident.

A witness who had previously corroborated that alibi disavowed the story when confronted with those records, the prosecutor said. That witness then told investigators that Prescott was in Boston at the time of the shooting.

Prosecutors approved a warrant for Prescott’s arrest on March 29. Boston Police arrested him May 17 in Newport News, Virginia, at the home of a friend’s brother. He was returned to Boston yesterday.

In a separate proceeding this afternoon, Assistant District Attorney Ian Polumbaum said that members of the Boston Police Cold Case Squad last year renewed the investigation into Gleason’s May 16, 1989, death during a stabbing inside a residence on School Street in Dorchester.

Detectives tracked down individuals who had been in that residence at the time and also examined Gleason’s clothing looking for biological evidence that might not have been tested at the time. Both avenues proved successful, Polumbaum said.

Criminalists found six bloodstains on Gleason’s jacket that, significantly, appeared to have originated on the outside of the garment, as opposed to have soaked outward from his 18 stab wounds. One of those bloodstains, he said, was tested and matched to Sutton’s unique DNA profile, on hand in a state database because of a prior felony conviction.

“Rather than being the only evidence in the case, it corroborates other evidence in the case,” Polumbaum said, noting that many of the original witnesses “were still around” and spoke to investigators.

Witness statements put Sutton at the School Street scene on the night of his homicide, the prosecutor said. The defendant had not only asked Gleason for money in the apartment but was overheard “demanding money from him.”

“The defendant was later seen walking away with what appeared to be blood on his face,” Polumbaum said.

The cases were very different in their fact patterns but the investigations shared a commonality, Conley said.

“We used high-technology forensic science and old-fashioned shoe leather detective work,” Conley said. “And we’ll use every tool at our disposal to find justice for these families, no matter how long it takes.”

Prescott will return to court on June 20 with attorney Elda James. Sutton will return to court on June 21 with attorney Timothy Bradl.