I found a reference to a very similar scenario here, but there's no accidental release:
Michael T. Osterholm, an epidemiologist and bioterrorism expert, and John Schwartz, science reporter at the New York Times, have outlined an anthrax bioterrorism scenario in their book Living Terrors: What America Needs to Know to Survive the Coming Bioterrorist Catastrophe.
In this scenario, the terrorist is a Russian immigrant in the United States, a former scientist from the Soviet Union biowarfare program. Yuri becomes unemployed when President Yeltsin closed a Biopreparat germ factory in Noviosibirsk. (Biopreparat was the name of the former Soviet Union's biowarfare program.) He is approved for a U.S. visa, and leaves Russia with a tiny sample of the smallpox virus, three miniature metal vials hidden inside a fountain pen. He is not afraid to smuggle it into the U.S., because he has already been vaccinated, and because he knows it will be worth an astronomical amount of money.
He is disappointed by his new homeland and has come to hate it. He was angry and lonely even back in the "good old days" in Russia, when he weaponized lethal germs for a living. Now, he is more than just a disappointed researcher. He is ready to commit terrorism.
Yuri makes an attempt to contact Middle Eastern terrorists by approaching an Arab organization in Chicago. They don't seem interested, but one day he finds an anonymous letter slipped under his door. The letter tells him he will soon earn big money.
A second note follows two days later, with instructions for meeting in a public place. After about an hour the two men have a deal. Yuri promises to get ready to deliver the smallpox virus, with seventy-two hours notice, at a place chosen by his client. The payment for this "little errand" is $50,000, just for starters.
He uses his small homemade laboratory to grow a smallpox culture in eggs from a local store. At Thanksgiving, he gets another message. This one tells him to deliver his deadly weapon at a large, well-known mall during the first day of Christmas shopping rush.
Yuri attaches an aerosolizer with a timer to a wall close to an air circulation vent. Half an hour later an invisible, odorless, thin mist of smallpox virus fills the seven-story building and thousands of shoppers will breathe it into their lungs. Many of the 100,000 shoppers who are visiting the mall will become like smallpox weapons themselves, unknowingly spreading the disease to others.
Search terms of russian smallpox pen mall -explosion (there's a smallpox lab in Russia that had an explosion which was dominating results).
