WPXI's Renee Kaminski asked Bridgeville Police Chief Chad King if he believed the Facebook post is what brought her in.
"Yes, it was pretty apparent her world was shrinking around her," King said.
In just one week, his unusual Facebook post pleading with Rosiek to turn herself in was viewed or shared by nearly three million people.
"I have known you since you were a teenager in Bridgeville. Let's end this foolishness - do the right thing and turn yourself in."
Police told WPXI last Christmas, Rosiek sold a fatal dose of what she advertised as heroin, but turned out to be fentanyl that led to Michael DeSanto's death.
"We had a lot of tips that were either called in by phone or sent in by Facebook and we were tracking them down," King said.
The chief added because of social media, police also found out where Rosiek and her boyfriend were staying and were about to move in, when they got a call from Rosiek's attorney who said she was going to turn herself in.
"We are cooperating, doing everything we can to get this resolved," her defense attorney, Justin Ketchel, said. "When everything is done, she's found to be vindicated of all these charges."