A Harwich man is facing an involuntary manslaughter charge for allegedly giving heroin laced with fentanyl to a friend who suffered a fatal overdose when they got high together last spring.

Luke Stratton, 25, was indicted on the charge Friday in Barnstable Superior Court, according to the Cape and Islands district attorney’s office. He’s charged with involuntary manslaughter for his alleged role in the overdose of Justin Saunders, 24, who died on March 26, 2017.

“It’s a good thing that we are raising awareness around this issue; you can be prosecuted for manslaughter for distributing drugs that kill people,’’ District Attorney Michael O’Keefe said, adding that his office has brought four manslaughter cases stemming from overdoses.

The government, O’Keefe said, must prove “beyond a reasonable doubt that the drugs that were given by defendant A were the drugs that killed victim B, and that’s what makes these cases very difficult to prove.’’

A lawyer for Stratton didn’t immediately return a call seeking comment. Stratton’s arraignment is scheduled for March 12.

He was initially arraigned on drug charges in district court, and the involuntary manslaughter indictment came after “further information was developed,’’ O’Keefe said. He declined to elaborate because the case is pending.

An affidavit in Stratton’s case filed by State Police Trooper Joshua J. Fries said Stratton called 911 after Saunders overdosed inside a Yarmouth home shortly before 3:40 p.m. on March 26.

The medical examiner later ruled that Saunders died from “acute ethanol and fentanyl intoxication,’’ and tan powder recovered from the scene tested positive for fentanyl, Fries wrote.

Stratton had also used some of the heroin and was treated at Cape Cod Hospital, where he spoke with investigators, the affidavit said.

Fries wrote that Stratton initially lied to police, claiming Saunders called for a ride at 2:30 p.m., and that he drove him to another location, where Saunders bought heroin from a dealer later identified as Christopher Schoener, 19.

Then, Stratton told police, he and Saunders returned to the Yarmouth home. Stratton said he stepped out momentarily to call his girlfriend, whose last name he didn’t know, and found Saunders slumped over when he went back inside.

But phone records told a different story, showing Saunders was “not looking for a ride’’ but “looking for Stratton to supply him with heroin/fentanyl,’’ Fries wrote.

In addition, while Stratton claimed Saunders bought the drugs from Schoener, phone records show Stratton called Schoener at 1:28 p.m. and at 2:02 p.m., the filing said, and Saunders made just one call that day, to a bank. Schoener’s number wasn’t programmed into Saunders’s phone, and records show they had no phone contact with one another in the hours before the overdose, according to the affidavit.

Stratton was also in contact with Schoener “one time’’ after Saunders’ death, the filing said.

“Investigators have concluded that Stratton, not Saunders, arranged to purchase heroin or fentanyl from Schoener and picked up the fentanyl to distribute it to Saunders,’’ Fries wrote.

A spokeswoman for O’Keefe said in an e-mail Thursday that Schoener has not been charged criminally in connection with the case. A number listed for Schoener was out of service Thursday.

O’Keefe said Thursday that gathering evidence to support a manslaughter charge can be difficult because the scene of a fatal overdose is often “cleaned’’ before first responders arrive.

“We make every effort to establish that chain of evidence that would allow us to bring a manslaughter case,’’ O’Keefe said. “But it is rare that we can meet that standard of proof beyond a reasonable doubt.’’

Travis Andersen can be reached at travis.andersen@globe.com.