Stephen Silva, who provided Boston marathon bomber Dzhokhar A. Tsarnaev the gun used to kill an MIT police officer in 2013, was released last Tuesday after a federal judge ruled he had spent sufficient time in prison.

In his testimony, Silva said he lent Tsarnaev, a childhood friend, an illegal gun that Tsarnaev said he would use to rob drug dealers from Rhode Island. Instead, the firearm was used to kill MIT police officer Sean A. Collier a few days after the Boston Marathon bombings in April 2013.

Silva was arrested in July 2014 on counts of heroin trafficking and possession of a gun with a defaced serial number, and eventually pleaded guilty to his charges. Silva’s arrest was unrelated to the Boston marathon bombings.

In the recent ruling, U.S. District Judge Mark L. Wolf said he had reduced Silva’s sentence because of his willingness to cooperate with prosecutors during Tsarnaev’s trial earlier this year. Indeed, Silva’s testimony during the trial offered a counterargument to the defense’s claim that Tsarnaev’s older brother, Tamerlan, was responsible for the operation and acquired the gun himself.

Silva had already served 17 months since his arrest in July 2014.

Prosecutors said Silva was unaware of the brothers’ plan to bomb the 2013 marathon, and Silva told the judge he regretted his actions. He also told reporters he wanted to offer “his deepest condolences” to the Collier family.

In June, Dzhokhar Tsarnaev was formally sentenced to death for his role in the 2013 Boston Marathon bombings, which left three dead and hundreds wounded. Days after Tsarnaev and his brother set off two pressure-cooker bombs near the marathon’s finish line, police cars raced across Cambridge in pursuit of the brothers, leading to a shootout that left Tamerlan dead. A subsequent manhunt for Tsarnaev left much of the Boston area, including Harvard, on lockdown, and Tsarnaev was eventually captured in Watertown.

The office of Judge Mark L. Wolf declined to comment on the ruling.

—Staff writer Beth Young can be reached at bethyoung@college.harvard.edu. Follow her on Twitter @thebethyoung.