MILL CREEK — Police believe they’ve put the city’s biggest heroin dealer behind bars.

And he’s likely to stay a while.

Richard Shanahan recently was sentenced to 30 years in state prison for trafficking drugs and stolen guns. The case started nearly a year ago, when police raided a Mill Creek storage unit and found heroin and more than 30 stolen firearms.

“That’s one of the largest, if not the largest, seizure of guns and drugs that we’ve had in this police department’s history,” Mill Creek officer Ian Durkee said.

The 30-year sentence, handed down in January, isn’t the end of Shanahan’s legal troubles, though. He’s due in federal court in June for sentencing in a separate bust involving drugs and guns.

In that case, out of Bothell, lawyers are expected to recommend 15 years, to overlap with his lengthier local sentence. However, Shanahan, 35, could face decades in federal prison, enough to amount to a life sentence. For now, he’s being held at a Seattle lockup.

Shanahan has been dealing drugs for most of his adult life. He’s sold heroin, methamphetamine and ecstasy, with convictions dating back to 2003.

His former girlfriend, Melanie Hebert, 31, was sent to prison in March for the Mill Creek case.

In storage units rented by the pair, detectives found ledgers tracking the sales of drugs and guns, including evidence that Shanahan was selling more than a pound of heroin a day, worth $40,000. Shanahan reportedly had 1.6 ounces of heroin in his pockets during the bust.

In 2013, Shanahan was found with a quarter-pound of heroin and a .40-caliber pistol. Later, in a guilty plea, he admitted he had the gun to further his drug dealing, court papers show.

In another case from 2013, Shanahan was pulled over in a “very expensive and brand new Cadillac” — it was stolen — and had three firearms, nearly $15,000 in cash and a variety of drugs including heroin.

Then, in a 2014 arrest, he had a pound of heroin, a pound of meth, and hundreds of prescription pills on him.

The Mill Creek investigation targeted a “very large enterprise” and “a very disturbing set of circumstances,” Snohomish County Superior Court Judge Ellen Fair said during a hearing last month.

Fair sentenced Hebert to nearly 3.5 years in prison, with credit for 10 months she spent in the Snohomish County Jail.

Hebert pleaded guilty to illegal gun possession. Her previous criminal history included five felonies and repeatedly failing to appear in court.

Hebert’s attorney, Kelly Canary, argued that she had “little or no knowledge” of Shanahan’s illegal activities, though the couple lived together for years.

Hebert chose not to know what was going on because of her extreme meth addiction, Canary said. “This is a person who is watching her life completely fall apart,” she said.

Judge Fair said it was “hard to swallow” that Hebert wasn’t actively involved in the drug operation.

Rikki King: 425-339-3449; rking@heraldnet.com.