“He suffered from depression,” Greg Shea said. “He was self-medicating.”

The Sheas knew who sold the drugs to their son, but when they asked police what could be done about it, they were crushed by the response: nothing.

Roughly half of the nation’s states have laws for drug-induced homicide, but Massachusetts is not one of them. Prosecutors can use the state’s manslaughter statute to charge drug dealers who sold fatal doses, but rarely do, especially after the Supreme Judicial Court in 2019 unanimously overturned the manslaughter conviction of a man who supplied heroin to a UMass Amherst student friend who died of an overdose.

Looking for justice for their son, the Sheas began asking why there isn’t a law tailored to go after a new breed of pushers selling lethal additives like fentanyl. They found a sympathetic ally in their state senator, Patrick O’Connor, a Weymouth Republican.

O’Connor is trying to fashion a law that gives prosecutors discretion to bring charges against dealers who sell lethal doses, especially those laced with fentanyl, which is responsible for the vast majority of overdose deaths in Massachusetts. O’Connor hopes to introduce the legislation this year.

O’Connor acknowledges that a drug-induced homicide law will be a tough sell in Massachusetts, where critics point to overreach in other states. But the senator believes Massachusetts can avoid the pitfalls that have occurred elsewhere.

“My office has done extensive research on what other states are doing, what are the best practices,” O’Connor said. “We can’t arrest our way out of this. We have to stress education. But there has to be an element of enforcement. Sometimes, there has to be an element of justice for these devastated families.”

The deadly scourge of fentanyl argues for a response different than the status quo. The state Department of Public Health found that fentanyl was present in some 94 percent of fatal overdose cases in the first six months of 2022. Finding the right balance between public health and law enforcement, however, is tricky.

“We have some of the best support systems for those with substance abuse disorder. The social component is there. The compassion is there,” O’Connor said. “Do we continue to turn a blind eye to families being destroyed, or do we give our DAs the tools to prosecute people, high-level dealers, who knowingly sell drugs that kill people.”

The bill he plans to introduce will carve out exceptions, including one for those who supply a drug but who summon help after an overdose.

“We’re not talking about going after family members, or friends, or those suffering from drug abuse themselves, or small-time dealers,” he said. “We’re talking about giving our district attorneys more tools to take mid- to high-level drug dealers off our streets.”

O’Connor is aware some drug-induced homicide laws have been too sweeping, charging marginal players instead of cynical, profit-driven dealers, and is determined to avoid those mistakes, and to ensure the law is applied equitably.

“The data needs to be dug into deeper,” he said. “We hope to address the racial injustice aspect of this with a commission and data gathering to make sure this is not used improperly.”

Plymouth District Attorney Tim Cruz, president of the Massachusetts District Attorneys Association, said the proliferation of fentanyl, and additives that are resistant to life-saving measures such as Narcan, merits adding more legal tools that can bring a measure of justice to families ruined by drugs.

Cruz said prosecutors will weigh in on the bill and agrees with O’Connor that it needs to target bigshots profiting off drugs that kill, not users involved in the drug trade to feed their own addiction. As with all prosecutions, discretion is key.

“If there is a better way to do our job, to help those who we can help, and pursue those we should pursue, we’re all in favor it,” Cruz said.